Calpastatin Activity Research Articles

Single nucleotide polymorphisms in Brahman steers and their association with carcass and tenderness traits

Data from purebred Brahman steers (N = 467) were used to study the association of single nucleotide polymorphisms (SNP) with carcass traits and measures of tenderness. Fall weaned calves were grazed and fed in a subtropical environment and then harvested for processing in a commercial facility. Carcass data were recorded 24 h postmortem. Muscle samples and primal ribs were obtained to measure calpastatin activity and shear force. DNA was used to determine genotypes of thyroglobulin (TG5), calpastatin (CAST) and mu-calpain (CAPN 316 and CAPN 4751) SNP. Minor allele frequencies for CAST, CAPN 316 and CAPN 4751 were 0.342, 0.031, and 0.051, respectively. CAST genotypes were associated with calpastatin enzyme activity (P < 0.01) and shear force of steaks aged for 14-day postmortem (P < 0.05). CAPN 316 genotypes were also associated with variation in shear force of steaks aged for 14 days (P < 0.05). CAPN 4751 genotypes approached significance for association with shear force of steaks after 7 and 14 days (P < 0.08). Genotypes for TG5 were non-polymorphic (i.e., minor allele frequency = 0.004) and omitted from further analyses. Neither CAST nor CAPN SNP was associated with variation in other carcass traits.

The comparison of three β-agonists for growth performance, carcass characteristics and meat quality of feedlot cattle

Forty-eight Bonsmara steers were assigned to three treatment groups and one control group consisting of 12 animals each. The control (C) received no β-agonist, while the three treatment groups received zilpaterol (6 ppm) (Z), ractopamine (30 ppm) (R) or clenbuterol (2 ppm) (Cl) for the last thirty days on feed. Growth performance (final 30 days), USDA quality and yield grades and meat quality (shear force, chemical, histological and biochemical) were compared for the three β-agonist and control groups. Animals responded negatively to Cl treatment during initial stages of supplementation, which was evident in lower feed consumption and initial growth rates. For carcass growth and yield, Cl had greater and more efficient growth rates, higher dressed out yields (proportional), lower USDA yield grades, and reduced marbling compared with C ( P < 0.05). For meat quality measurements, the M. longissimus (LL) and M. semitendinosus (ST) were sampled. Cl had the greatest effect ( P < 0.05) on WBSF, especially on the LL, followed by Z. Variation in tenderness and ageing effects corresponded with variation in calpastatin activity and myofibrillar fragmentation between treatment groups. While zilpaterol and ractopamine are currently the only products registered for cattle in different countries, it seems that zilpaterol has an advantage in carcass growth efficiency and yield without showing any adaptation problems for animals such as experienced by the more aggressive β-agonist clenbuterol.

Effects of postmortem carcass electrical stimulation on goat meat quality characteristics

Electrical stimulation (ES) has been reported to improve meat quality, but the effects of postmortem ES have not been fully characterized in goats. This experiment was conducted to determine the effects of postmortem ES on meat quality in two breeds of goats. Uncastrated Spanish and crossbreds (Boer × Spanish females × Kiko male) yearlings ( n = 10/breed, body weight 31.2 ± 2.43 kg) were transported to the slaughter facility, held overnight in pens without feed, and slaughtered on two different days. Immediately after slaughter each carcass was split into two halves along the vertebral column. The left half was subjected to a high voltage ES (580 V) at 5 s intervals during 120 s (treatment) and the right half was kept as a non-stimulated control. After 24 h of cooler storage (2 °C), the carcasses were fabricated into 2.5 cm-thick loin/rib chops. Longissimus dorsi (LD) muscle pH and temperatures were recorded at 0, 1, 2, 3, 4, 5, 6, 9, 12, 15, 18, and 24 h postmortem. The pH values of LD muscle were lower in stimulated sides than control sides ( P < 0.01), and pH decreased quadratically ( P < 0.01) with advancing time during the 24 h postmortem period. Treatment had no significant effect on the LD muscle temperature, and the temperature decline followed a cubic pattern ( P < 0.01) during the 24 h postmortem period. Muscle glycogen concentrations immediately after electrical stimulation (0 h) were lower ( P < 0.05) in the stimulated sides compared to control sides. Warner-Bratzler shear force (WBSF) values of loin chops were lower ( P < 0.01) in stimulated sides (3.0 kg) compared to control sides (4.2 kg), and the chops from Spanish goats (3.9 kg) had higher ( P < 0.05) WBSF values compared with crossbreds (3.3 kg). Color values ( L*, a*, b*, chroma, and hue angle) and sarcomere length were not affected by ES or breed. Heated calpastatin activities were not influenced by ES, but the activities were lower at day 4 compared with day 1 of aging ( P < 0.05). There were no significant effects ( P > 0.05) of ES or aging time on selected myofibrillar protein concentrations (myosin heavy chain, myomesin, desmin, actin, troponin-T, and myosin light chain, P > 0.05). However, desmin concentration tended to decrease at day 4 of aging ( P = 0.08). The results indicate that ES significantly accelerated postmortem glycolysis and improved tenderness of loin chops, as indicated by WBSF values.

Use of 25-hydroxyvitamin D3 and dietary calcium to improve tenderness of beef from the round of beef cows1,2

The objective of this trial was to determine how 25-hydroxyvitamin D(3) (25-OH D(3)) supplementation, altering supplemental dietary calcium, or their combination influence postmortem biochemical and tenderness changes in muscles from the round of mature cows. Twenty-seven Angus cows (3 to 7 yr old) were allotted randomly to 9 pens with 3 cows per pen. Treatments were arranged in a 3 x 3 factorial design with 3 dosages of 25-OH D(3) (0, 250, or 500 mg of 25-OH D(3) administered as a 1-time oral bolus 7 d before slaughter) and 3 percentages of supplemental limestone (0.5, 0.75, and 1.0%) replenished in the diet for 3 d before slaughter and after a 2-wk limestone withdrawal. Plasma samples were obtained during the feeding period. Upon slaughter, adductor, gracilus, pectineus, sartorius, semimembranosus, vastus intermedius, and vastus lateralis muscles were obtained and aged for 1, 3, or 7 d. Calcium concentrations were increased in plasma when 250 or 500 mg of 25-OH D(3) were administered (P </= 0.05). Calcium concentrations in muscle increased (P </= 0.001) when 500 mg of 25-OH D(3) were administered. Concentrations of 25-OH D(3) in meat and in plasma and 1,25-dihydroxyvitamin D(3) [1,25-(OH)(2) D(3)] in plasma were increased when 25-OH D(3) was administered (P </= 0.05). The percentage of limestone replenished in the diet had no effect on 25-OH D(3) or 1,25-(OH)(2) D(3) in meat or in plasma. Calpastatin activity was affected by treatments only in the gracilus and vastus intermedius muscles (P </= 0.05). Among all muscles and aging periods, calpastatin activity and intensity of troponin-T degradation product were related inversely. Results indicate that supplemental 25-OH D(3) has some influence on muscle characteristics known to improve tenderness, but improved tenderness was not observed.

Effect of two dietary concentrate levels on tenderness, calpain and calpastatin activities, and carcass merit in Waguli and Brahman steers1

The objective of this study was to compare carcass characteristics of a newly introduced breed, the Waguli (Wagyu x Tuli), with the carcass characteristics of the Brahman breed. Brahman cattle are used extensively in the Southwest of the United States because of their tolerance to adverse environmental conditions. However, Brahman carcasses are discounted according to the height of their humps because of meat tenderness issues. The Waguli was developed in an attempt to obtain a breed that retained the heat tolerance of the Brahman but had meat quality attributes similar to the Wagyu. Twenty-four animals were used. Six steers from each breed were fed a 94% concentrate diet and 6 steers from each breed were fed an 86% concentrate diet. Eight steers, 2 from each group, were harvested after 128 d, after 142 d, and after 156 d on feed. Waguli steers had larger LM, greater backfat thickness, greater marbling scores, and greater quality grades than the Brahman steers (P < 0.05). The Japanese Wagyu breed is well known for its highly marbled and tender meat, and these traits are also present in the Waguli. The Waguli had significantly lower Warner-Bratzler shear force values than the Brahman steers after 7 and 10 d of postmortem aging (P < 0.05); this difference decreased after 14 d postmortem (P = 0.2), when tenderness of the slower aging Brahman had increased to acceptable levels. Toughness of the Brahman has been associated with high levels of calpastatin in Brahman muscle, and the Waguli LM had significantly less calpastatin activity (P = 0.02) at 0 h postmortem than the Brahman LM. At 0-h postmortem, the total LM calpain activity did not differ between the Brahman and Waguli (P = 0.57). Neither diet nor days on feed had any significant effect on the 0-h postmortem calpain or at 0-h postmortem calpastatin activity, nor an effect on Warner-Bratzler shear-force values. In conclusion, LM muscle from the Waguli steers had a high degree of marbling, lower shear force values, and low calpastatin activity, all of which are related to more tender meat.

Enhanced efficiency of a capillary-based biosensor over an optical fiber biosensor for detecting calpastatin

A capillary-based optical biosensor has been developed to detect calpastatin, an indicator of meat tenderness. Longissimus muscle samples ( n = 11) were extracted from beef carcasses at 0 and 48 h post-mortem. These samples were assayed for calpastatin by traditional laboratory methods and with a newly developed capillary tube biosensor as well as for Warner–Bratzler shear force (WBSF) and crude protein and the responses were compared. Additionally, the response from the capillary-based biosensor was compared to a previously developed optical fiber biosensor. When the 0 and 48 h sampling periods were combined, the capillary tube biosensor was moderately accurate in predicting calpastatin activity ( R 2 = 0.6058). There was less variation in the 0 h capillary tube biosensor compared to the 0 h pre-column ( P = 0.006) and post-column optical fiber biosensors ( P = 0.047), therefore the capillary tube biosensor is a more precise system of measurement. This research further advances the development of a calpastatin biosensor and makes online assessment one step closer to reality.

Correlation between a novel calpastatin biosensor and traditional calpastatin assay techniques

An optical fiber biosensor to detect calpastatin has been investigated as a preliminary step in developing tenderness detection instrumentation. Longissimus dorsi samples were taken from beef carcasses (n=21) at 0, 24, 36 and 48h postmortem. Muscle homogenates were assayed for calpastatin activity using traditional methods and an optical fiber biosensor. Warner–Bratzler shear force was also performed on a steak from each carcass at 14d postmortem. Results demonstrated that the measurements with highest correlation between traditional calpastatin assays and optical biosensor readings were taken at 48h postmortem (r=0.597, P≤0.01), suggesting that this is the best time for use of this biosensor in an on-line grading system. This research further advances the development of a calpastatin biosensor and would be useful in laboratory determination of the presence of biologically active calpastatin concentrations.

Isolation and characterization of μ-calpain, m-calpain, and calpastatin from postmortem muscle. I. Initial steps1

Evidence has indicated that mu-calpain, m-calpain, and calpastatin have important roles in the proteolytic degradation that results in postmortem tenderization. Simple assays of these 3 proteins at different times postmortem, however, has shown that calpastatin and mu-calpain both rapidly lose their activity during postmortem storage, so that proteolytic activity of mu-calpain is nearly zero after 3 d postmortem, even when assayed at pH 7.5 and 25 degrees C, and ability of calpastatin to inhibit the calpains is 30% or less of its ability when assayed at death. m-Calpain, however, retains much of its proteolytic activity during postmortem storage, but the Ca(2+) requirement of m-calpain is much higher than that reported to exist in postmortem muscle. Consequently, it is unclear how the calpain system functions in postmortem muscle. To clarify this issue, we have initiated attempts to purify the 2 calpains and calpastatin from bovine semitendinosus muscle after 11-13 d postmortem. The known properties of the calpains and calpastatin in postmortem muscle have important effects on approaches that can be used to purify them. A hexyl-TSK hydrophobic interaction column is a critical first step in separating calpastatin from the 2 calpains in postmortem muscle. Dot-blot assays were used to detect proteolytically inactive mu-calpain. After 2 column chromatographic steps, 5 fractions can be identified: 1) calpastatin I that does not bind to an anion-exchange matrix, that does not completely inhibit the calpains, and that consists of small polypeptides <60 kDa; 2) calpastatin II that binds weakly to an anion-exchange matrix and that contains polypeptides <60 kDa; all these polypeptides are smaller than the native 115- to 125-kDa skeletal muscle calpastatin; 3) proteolytically active mu-calpain even though very little mu-calpain activity can be detected in zymogram assays of muscle extracts from 11- to 13-d postmortem muscle; this mu-calpain has an autolyzed 76-kDa large subunit but the small subunit consists of 24-, 26- and a small amount of unautolyzed 28-kDa polypeptides; 4) proteolytically active m-calpain that is not autolyzed; and 5) proteolytically inactive mu-calpain whose large subunit is autolyzed to a 76-kDa polypeptide and whose small subunit contains polypeptides similar to the proteolytically active mu-calpain. Hence, loss of calpastatin activity in postmortem muscle is due to its degradation, but the cause of the loss of mu-calpain activity remains unknown.

Neuroprotective mechanism of taurine due to up-regulating calpastatin and down-regulating calpain and caspase-3 during focal cerebral ischemia.

Taurine as an endogenous substance possesses a number of cytoprotective properties. In the study, we have evaluated the neuroprotective effect of taurine and investigated whether taurine exerted neuroprotection through affecting calpain/calpastatin or caspase-3 actions during focal cerebral ischemia, since calpain and caspase-3 play central roles in ischemic neuronal death. Male Sprague-Dawley rats were subjected to 2 h of middle cerebral artery occlusion (MCAo), and 22 h of reperfusion. Taurine was administrated intravenously 1 h after MCAo. The dose-responses of taurine to MCAo were determined. Next, the effects of taurine on the activities of calpain, calpastatin and caspase-3, the levels of calpastatin, microtubule-associated protein-2 (MAP-2) and alphaII-spectrin, and the apoptotic cell death in penumbra were evaluated. Taurine reduced neurological deficits and decreased the infarct volume 24 h after MCAo in a dose-dependent manner. Treatment with 50 mg/kg of taurine significantly increased the calpastatin protein levels and activities, and markedly reduced the m-calpain and caspase-3 activities in penumbra 24 h after MCAo, however, it had no significant effect on mu-calpain activity. Moreover, taurine significantly increased the MAP-2 and alphaII-spectrin protein levels, and markedly reduced the ischemia-induced TUNEL staining positive score within penumbra 24 h after MCAo. Our data demonstrate the dose-dependent neuroprotection of taurine against transient focal cerebral ischemia, and suggest that one of protective mechanisms of taurine against ischemia may be blocking the m-calpain and caspase-3-mediated apoptotic cell death pathways.

Effect of High Pressure on the Calpain–Calpastatin System in Fish Muscle

Calpains (calcium-activated neutral proteases) of sea bass (Dicentrarchus labrax L.) muscle may participate in the degradation of muscle tissue during postmortem storage. These enzymes are regulated by calpastatin, their endogenous specific inhibitor. The objective of this study was to evaluate the changes encountered by the calpain system during the postmortem storage of fish muscle after high-pressure treatment. From 100 MPa, high-pressure treatment of purified calpains results in a loss of their activity as well as in the dissociation of the heterodimeric form. In muscle, the high-pressure processing decreases the initial activity of calpain. This loss in activity may be due to an inactivation by a change of structure. Initial calpastatin activity is not modified by the high-pressure treatment, but it decreases during the storage from the beginning for a treatment at 300 MPa after which calpastatin is stable during 2 d. Therefore, this study also suggests that high-pressure treatment could be a useful way to improve fish flesh quality.

Protease activity higher in postmortem water buffalo meat than Brahman beef

We previously demonstrated that postmortem water buffalo meat had higher tenderness than Brahman beef. In order to explain this difference in tenderness, the objective of the current study was to investigate the protease activity in these two meats. Five female crossbred water buffalo (Philippine Carabao × Bulgarian Murrah) and five female crossbred cattle (Brahman × Philippine Native) were slaughtered at 30 months of age, followed by immediate sampling of Longissimus thoracis muscle for measurement of protease activity. Results showed that buffalo meat had significantly higher protease activity compared to beef ( P < 0.05). Furthermore, calpain inhibitor 1, a specific inhibitor of calpains 1 and 2, was the most effective inhibitor of protease activity. There was no difference in calpastatin activity, and no major differences were observed in calpains 1, 2, and calpastatin expression by Western blotting. This study suggests that higher calpain activity in early postmortem buffalo meat was responsible for the increased tenderness of water buffalo meat compared to beef.

Calpain/calpastatin activities and substrate depletion patterns during hindlimb unweighting and reweighting in skeletal muscle

Unloading of skeletal muscle by hindlimb unweighting (HU) is characterized by atrophy, protein loss, and an elevation in intracellular Ca(2+) levels that may be sufficient to activate Ca(2+)-dependent proteases (calpains). In this study, we investigated the time course of calpain activation and the depletion pattern of a specific structural protein (desmin) with unloading and subsequent reweighting. Rats underwent 12 h, 24 h, 72 h or 9 days of HU, followed by reweighting for either 0, 12 or 24 h. Total calpain-like activity was elevated with HU in skeletal muscle (P < 0.05) and was further enhanced with reweighting (P < 0.05). The increases in calpain-like activity were associated with a proportional increase in activity of the particulate fraction (P < 0.05). Activity of the mu-calpain isoform was elevated with 12 and 24 h of HU (P < 0.05) and returned to control levels thereafter. With reweighting, activities of mu-calpain were elevated above control levels for all HU groups except 9 days (P < 0.05). In contrast, minimal changes in m-calpain and calpastatin activity were observed with HU and reweighting. Although desmin depletion levels did not reach statistical significance, a significant inverse relationship was found between the mu-calpain/calpastatin ratio and the amount of desmin in isolated myofibrils (R = -0.83, P < 0.001). The results suggest that calpain activation is an early event during unloading in skeletal muscle, and that the majority of the increase in calpain activity can be attributed to the micro-isoform.

Genetic parameters for growth and carcass traits of Brahman steers1,2

Spring-born purebred Brahman bull calves (n = 467) with known pedigrees, sired by 68 bulls in 17 private herds in Louisiana, were purchased at weaning from 1996 through 2000 to study variation in growth, carcass, and tenderness traits. After purchase, calves were processed for stocker grazing on ryegrass, fed in a south Texas feedlot, and processed in a commercial facility. Carcass data were recorded 24 h postmortem. Muscle samples and primal ribs were taken to measure calpastatin activity and shear force. An animal model was used to estimate heritability, genetic correlations, and sire EPD. Relatively high heritability estimates were found for BW at slaughter (0.59 +/- 0.16), HCW (0.57 +/- 0.15), LM area (0.50 +/- 0.16), yield grade (0.46 +/- 0.17), calpastatin enzyme activity (0.45 +/- 0.17), and carcass quality grade (0.42 +/- 0.16); moderate heritability estimates were found for hump height (0.38 +/- 0.16), marbling score (0.37 +/- 0.16), backfat thickness (0.36 +/- 0.17), feedlot ADG (0.33 +/- 0.14), 7-d shear force (0.29 +/- 0.14), and 14-d shear force (0.20 +/- 0.11); relatively low heritability estimates were found for skeletal maturity (0.10 +/- 0.10), lean maturity (0.00 +/- 0.07), and percent KPH (0.00 +/- 0.07). Most genetic correlations were between -0.50 and +0.50. Other genetic correlations were 0.74 +/- 0.27 between calpastatin activity and 7-d shear force, 0.72 +/- 0.25 between calpastatin activity and 14-d shear force, (0.90 +/- 0.30 between yield grade and 7-d shear force, and -0.82 +/- 0.27 between backfat thickness and 7-d shear force. Heritability estimates and genetic correlations for most traits were similar to estimates reported in the literature. Sire EPD ranges for carcass traits approached those reported for sires in other breeds. The magnitude of heritability estimates suggests that improvement in carcass yield, carcass quality, and consumer acceptance traits can be made within the Brahman population.

CHANGES IN THE CALPAIN-CALPASTATIN AND CATHEPSIN (B, B+L, H AND D) DURING POSTMORTEM STORAGE OF GOAT MUSCLES

The objective of this study was to elucidate a relationship between some endogenous proteinases and their inhibitors in four different goat muscles during postmortem storage. Samples were taken from the longissimus dorsi (LD), biceps femoris (BF), semimembranosus (SM) and semitendinosus (ST) muscles stored up to 20 days postmortem at 5C. Activities of calpain-I, calpain-II, calpastatin, cathepsins (B, B+L, H and D) and cystatin(s) were determined. Decreases in calpain-I and calpastatin activities were significantly more than that of calpain-II activity. The cathepsin B, B+L, H and cystatin level were found to fall by 9-35% after 20 days, whereas the cathepsin D showed 11-17% decline in all the muscles. Thus changes in muscle proteinases and their inhibitors during postmortem storage differ and the results may shed light on their role in myofibrillar proteolysis and goat meat tenderization. L'importance de la proteolyse post mortem differe dans la viande de chevre selon le type de muscle. L'objectif de cette etude est de determiner les relations entre les proteinases endogenes calpaines (I et II) et cathepsines (B, B+L, H and D) et leurs inhibiteurs comme la cystatine et la calpastatine, dans 4 muscles differents de la chevre pendant un entreposage post mortem de 20 jours a 5°C. Les differences mises en evidence dans les activites de la cathepsine B+L, cystatine, calpaine I et calpastatine sont responsables des differences observees dans la proteolyse des muscles de chevre.

The Hypertrophic Marchigiana: physical and biochemical parameters for meat quality evaluation

The aim of this study was to evaluate the meat quality of double muscled Marchigiana young bulls characterized by different genotypes for the hypertrophy: normal and mutated (heterozygous). Calpain and calpastatin activities were determined to verify the state of aging meat on a sample of Longissimus thoracis muscle (XIII thoracic rib) taken at slaughtering (0h) and after 24 hours (24h). After 14 days of aging, another sample of muscle was taken to evaluate physical and chemical parameters of meat quality. The results showed a better meat quality of mutated animals respect normal animals. Another interesting result was the correlation between the biochemical parameters and some physical parameters, such as WBS (Warner Bratzler Shear Force), CL (Cooking loss). These results showed the relationship between the proteolytic activity of calpain system and meat tenderness.

Postmortem Metabolic Rate and Calpain System Activities on BeefLongissimusTenderness Classifications

In this study, we adopted a model of tenderness classification in order to determine the factors affecting the tenderness and tenderization characteristics of beef longissimus, using cluster analysis on the basis of Warner-Bratzler shear force and myofibril fragmentation index, at 1, 7, and 14 d. The rate of tenderization was effectively differentiated by pH, R-values, mu-calpain activity, and calpastatin activity. Differences among tenderness classes were generally detected at 3 and 9 h postmortem for metabolic rate, and at 9 and 24 h for the activities of mu-calpain and calpastatin. Early postmortem metabolic rate and calpain system activities were verified as important factors with regard to longissimus tenderization.

EFFECTS OF MUSCLE PROTEASES, ENDOGENOUS PROTEASE INHIBITORS AND MYOFIBRIL FRAGMENTATION ON POSTMORTEM AGING OF GOAT MEAT

The present study was conducted to evaluate the extent of postmortem proteolysis in longissimus dorsi, biceps femoris, semimembranosus and semi-tendinosus goat muscles on postmortem aging at an ambient (27C) temperature. The activities of calpains and calpastatin were determined after separation on a (diethylamina )ethyl-Sephacel column (Sigma, St. Louis, MO) and cathepsin (B, B + L and H) by carboxymethyl-Sepharose column (Sigma). The results showed that the decrease in calpain land calpastatin activities was significantly higher than that of calpain II. Cathepsin B, B + L, H and cystatin were found to fall by 30-80% after 12 h, whereas cathepsin D decreased significantly in all the muscles. The disappearance of titin 1 and nebulin, and the appearance of a 30-kDa component were confirmed by Western blot analysis. The appearance of the 30-kDa component reported here explains the time-induced structural changes of myofibrils. The Z-line degradation had occurred by 6 h postmortem. Cathepsins are not stable compared to calpains during postmortem aging, and both enzymes may play a significant role in the proteolysis of myofibrillar proteins at ambient temperature.

Residual feed intake of purebred Angus steers: Effects on meat quality and palatability

Relationships between residual feed intake (RFI) and other performance variables were determined using 54 purebred Angus steers. Individual feed intake and BW gain were recorded during a 70-d post-weaning period to calculate RFI. After the 70-d post-weaning test, steers were fed a finishing ration to a similar fat thickness (FT), transported to a commercial facility, and slaughtered. A subsample of carcasses (n = 32) was selected to examine the relationships among RFI, meat quality, and palatability. Steers were categorized into high (> 0.5 SD above the mean; n = 16), medium (mid; +/- 0.5 SD from the mean; n = 21), and low (< 0.5 SD below the mean; n = 17) RFI groups. No differences were detected in ADG, initial BW, and d 71 BW among the high, mid, and low RFI steers. Steers from the high RFI group had a greater DMI (P = 0.004) and feed conversion ratio (FCR; DMI:ADG; P = 0.002) compared with the low RFI steers. Residual feed intake was positively correlated with DMI (r = 0.54; P = 0.003) and FCR (r = 0.42; P = 0.002), but not with initial BW, d 71 BW, d 71 ultrasound FT, initial ultrasound LM area, d 71 ultrasound LM area, or ADG. The FCR was positively correlated with initial BW (r = 0.46; P = 0.0005), d 71 BW (r = 0.34; P = 0.01), and DMI (r = 0.40; P = 0.003) and was negatively correlated with ADG (r = -0.65; P = 0.001). There were no differences among RFI groups for HCW, LM area, FT, KPH, USDA yield grade, marbling score, or quality grade. Reflectance color b* scores of steaks from high RFI steers were greater (P = 0.02) than those from low RFI steers. There was no difference between high and low RFI groups for LM calpastatin activity. Warner-Bratzler shear force and sensory panel tenderness and flavor scores of steaks were similar across RFI groups. Steaks from high RFI steers had lower (P = 0.04) off-flavor scores than those from low RFI steers. Cook loss percentages were greater (P = 0.005) for steaks from low RFI steers than for those from mid RFI steers. These data support current views that RFI is independent of ADG, but is correlated with DMI and FCR. Importantly, the data also support the hypothesis that there is no relationship between RFI and beef quality in purebred Angus steers.

Factors influencing the variation in tenderness of seven major beef muscles from three Angus and Brahman breed crosses

Beef carcasses ( n = 30) from 3/4 Angus (A) × 1/4 Brahman (B), 1/4A × 3/4B, and 1/2A × 1/2B F 1 crosses were used to evaluate breed type, electrical stimulation, and postmortem aging on the M. semimembranosus (SM), M. semitendinosus (ST), M. biceps femoris (BF), M. vastus lateralis (VL), M. gluteus medius (GM), M. longissimus dorsi lumborum (LD), and M. triceps brachii (TB). Shear force values decreased with increased postmortem aging to a greater extent in steaks from 3/4A × 1/4B than steaks from the other breed types. Shear force values for steaks from the round (SM, ST, BF, VL) were higher than steaks from the loin (LD, GM) and chuck (TB) for both electrically stimulated and non-electrically stimulated muscles. In the LD muscle, calpastatin activities were similar among breed types. Muscle type played the greatest role in determining tenderness.

The Calpain System in Muscular Dystrophy

The muscular dystrophies cause progressive muscle wasting leading to decreased ability to function physically and even death. A large amount of evidence suggests that the calpain system is involved in the muscle wasting associated with these diseases. Calpains are Ca2+-activated proteases and intracellular [Ca2+] is elevated 2-4-fold in dystrophic muscle. The increased [Ca2+] may result in unregulated calpain activity and increased protein degradation. The calpain system in skeletal muscle consists of 3 proteins: 1) μ-calpain, a protease requiring 3–50 μM Ca2+ for half-maximal activity; 2) m-calpain, a protease requiring 400–800 μM Ca2+ for half-maximal activity; and 3) calpastatin, a specific protein inhibitor of μ- and m-calpain. The goal of this project is to characterize these proteins in human dystrophic skeletal muscle. We have developed a protocol for analysis of μ-calpain, m-calpain, and calpastatin from a 200–800 mg biopsy sample. Samples were obtained at the University Medical Center. Biochemical analysis of the soluble proteins included casein zymography, western blotting, enzymatic activity assays, inhibitor assays, and ELISA. In nearly every sample analyzed so far, the calpastatin activity in the crude supernatant is 5–20-fold higher than the calpain activity. However, once separated, the calpain activity appears to be higher than the calpastatin activity. This may indicate that the calpastatin in the dystrophic muscle samples is unable to inhibit the endogenous calpain activity. Supported by NRI 2002-35206-11630, 2004-04338, and the MDA.