Proteolysis Index Research Articles

Chick skeletal muscle proteolysis in vitro increased by corticosterone.

Six-day-old chick skeletal muscle (extensor digitorum longus) was incubated in the presence of corticosterone (CTC; 0, 3, 30, and 300 ng/ml) for 2 h at 37 degrees C. Tyrosine and N (tau)-methylhistidine releases, as indices of total muscle and myofibrillar proteolysis, were increased by CTC but with different dose responses, indicating an independent regulation of myofibrillar and non-myofibrillar protein degradation.

Changes in the physicochemical properties and organoleptic quality of galician chorizos during curing and after vacuum-packing

Galician chorizo is a spicy smoked pork sausage made in northwest Spain. In the work reported here, physicochemical properties and organoleptic quality were evaluated (a) during manufacture and curing and (b) during storage of chorizos vacuum-packed after curing for 18 or 30 days. During curing, pH initially declined and then rose again; this pattern was reflected in an increase in acid flavour. Moisture content and water activity declined, while hardness increased, as reflected in the observed reduction in juiciness and the observed increase in subjectively-perceived hardness. Acidity index, peroxide index and proteolysis index increased only slightly over the curing period, and the tasters did not detect any organoleptic changes attributable to changes in these variables. During storage after vacuum-packing, no significant changes were observed in moisture content, water activity or hardness, but pH, acidity index, peroxide index and proteolysis index all increased gradually. During the last two weeks of storage of chorizos packed on day 30 of curing, tasters detected both rancid and strange flavours.

Analysis of whey proteins during ripening of Afuega'l Pitu cheese by reversed phase HPLC Análisis por RP-HPLC de las proteínas del suero del queso Afuega'l Pitu durante la maduración

Evolution of the whey proteins fractions and proteolysis indices from 12 batches of the artisan cheese Afuega'l Pitu variety were studied by reversed phase high performance liquid chro matography (RP-HPLC) over the ripening period. The correlation coefficients between the whey protein contents and ripening time were very low, indicating that the whey protein content did not change as the cheese aged. However, soluble nitrogen content and the percentage of total nitrogen in the soluble form showed correlation coefficients higher than 0.9 with increasing ripening time. Analysis of variance showed significant differences ( p < 0.05) between dairies for most of the variables with the exception of β-lactoglobulin A and bovine serum albumin. These variables were also significantly different between the two manufacture zones. Conversely, no significant differences ( p < 0.05) were observed between the two varieties of cheese, red and white, for whey protein content or for proteolysis indices.

Electrophoretic ripening index for the evaluation of proteolysis and the deduction of the age of Parmesan cheese

We have established an electrophoretic method to evaluate proteolysis in Parmesan cheese by means of an objective ripening index. The separation of caseins by alkaline polyacrylamide gel electrophoresis (PAGE) (12% T, 2.6% C, pH 8.9, 5 M urea) is followed by the densitometric analysis of theγ- andβ-casein fractions. The relationship between the resulting coefficients (γ-Cn/β-Cn) and the age of reference samples of Original Italian Grana Padano (6–22 months) was linear up to 15 months, allowing an evaluation of the extent of proteolysis and therefore a deduction of the age of the Parmesan samples analysed. Based on this calibration we propose to use a threshold level of 1.3 (γ-Cn/β-Cn) to verify the required age, i.e. 12 months, of Parmesan cheese, retailed as a loaf or prepacked slices. Commercially grated Parmesan samples may contain ≤20% cheese rind, which has a very low degree of casein breakdown. So a threshold level of 0.8 (γ-Cn/β-Cn) is proposed for all grated Parmesan products. The preparation of reference solutions with defined coefficients (γ-Cn/β-Cn), corresponding to the proteolysis indices of reference samples of different aged Grana Padano is described. The coefficients (γ-Cn/β-Cn) as well as theβ-casein content of two additional series of reference samples and of 49 commercial Parmesan samples taken from retail outlets in Austria and Italy are presented.

The Effect of Liposome-Encapsulated Cyprosins on Manchego Cheese Ripening

Cyprosins, the proteinases present in cardoon rennet, were extracted from dried flowers of cardoon (Cynara cardunculus L.) and encapsulated in dehydration-rehydration liposomes. Liposomes were added to pasteurized ovine milk to accelerate the ripening of Manchego cheese. Encapsulated proteinases had no effect on whey composition, but DM and protein content were lower in 1-d-old experimental cheese than in the respective control cheese. Enhancement of proteolysis by encapsulated cyprosins was evident 24h after manufacture; 38.3% of αs-CN and 47.7% of β-CN that were initially present in milk had been degraded in l-d-old experimental cheese and 20.3 and 37.5%, respectively, in control cheese. At that time, amounts of N that were soluble at pH 4.6, in TCA, and in phosphotungstic acid were 15.70, 5.47, and 2.09% in experimental cheese and 9.32, 4.16, and 1.34% in control cheese, respectively. The hydrophobic and hydrophilic peptides that were separated by HPLC and measured at 214 and 280nm, and their ratio, were also higher in experimental cheese than in control cheese on d 1. However, some of the indices of proteolysis were higher in control cheese than in experimental cheese after 60 d of ripening. Experimental cheese was softer than control cheese 24h after manufacture, but texture was not different thereafter. Addition of encapsulated cyprosins to milk perceptibly accelerated development of flavor intensity in experimental cheese through 15 d of age without enhancing bitterness.

Differential responsiveness of protein synthesis and degradation to amino acid availability in humans.

We investigated the effects of graded hyperaminoacidemia on protein metabolism in eight healthy, young (25 +/- 2 years), normal weight (BMI = 25 +/- 1 kg/m2), overnight-fasted human subjects. A balanced amino acid solution was infused for 180 min at five different rates: 0.5 (study I), 1.0 (study II), 2.0 (study III), 4.0 (study IV). and 6.0 (study V) mg x kg-1 x min-1 on separate days in random order. Studies were performed with [1-14C]leucine infusion and indirect calorimetry to calculate leucine oxidation (LOX), nonoxidative leucine disposal (NOLD) (an index of protein synthesis), and endogenous leucine flux (ELF) (an index of proteolysis). Basal total plasma amino acid concentrations averaged 1.85 +/- 0.1 mmol/l and increased to 2.27 +/- 0.1, 2.70 +/- 0.2, 3.84 +/- 0.2, 5.87 +/- 0.4, and 7.52 +/- 0.3 mmol/l in studies I-V, respectively. ELF decreased from a basal value of 2.27 +/- 0.2 to 2.12 +/- 0.2, 1.97 +/- 0.1, 1.73 +/- 0.2, 1.67 +/- 0.3, and 1.65 +/- 0.1 micromol x kg-1 x min-1 in studies I-V, respectively (P < 0.05 for study I vs. basal, P < 0.01 for studies II-V vs. basal, and NS for studies IV and V vs. study III). LOX increased from a basal value of 0.31 +/- 0.04 to 0.38 +/- 0.05, 0.41 +/- 0.02, 0.64 +/- 0.04, 1.11 +/- 0.07, and 1.56 +/- 0.05 micromol x kg-1 x min-1 in studies I-V (all P < 0.01 vs. basal; P < 0.05-0.01 for each study vs. preceding study). Basal NOLD averaged 1.96 +/- 0.2 and did not change significantly in studies I and II (2.03 +/- 0.2 and 2.10 +/- 0.1 micromol x kg-1 x min-1). In contrast, a significant increase in NOLD was observed in studies III, IV, and V (to 2.3 +/- 0.15, 2.74 +/- 0.2, and 3.25 +/- 0.7 micromol x kg-1 x min-1, respectively; all P < 0.01 vs. basal; P < 0.05-0.01 for each study vs. preceding study). The net leucine balance (difference between ELF and NOLD)(-0.31 +/- 0.06 micromol x kg-1 x min-1) became less negative in study I (P < 0.01 vs. basal) and positive during studies II-V when the rise in plasma total amino acid levels was >/= 50% above basal level (P < 0.01 vs. each preceding study). In conclusion, NOLD, ELF, and LOX exhibit a differential responsiveness to acute changes in substrate availability: 1) small increments (25-50%) in plasma amino acid levels inhibit ELF and stimulate LOX but have no effect on NOLD; 2) stimulation of NOLD is observed only with increments in plasma amino acid levels >/= 100% above basal values; and 3) increments in plasma amino acid concentrations > 100% above basal values cause a progressive dose-related increase in LOX and NOLD but do not induce any further inhibition of ELF.

Effects of Aging Time and Temperature on Proteolysis of Commercial Goat Milk Cheeses Produced in the United States

We evaluated the effects of aging time and temperature on proteolytic indices of freshly prepared commercial cheeses from goat milk. Five varieties of cheeses from goat milk (plain soft, pepper soft, Caciotta, Monterey Jack, and raw milk Cheddar) and two from cow milk (one fresh and one 2-mo-old Cheddar) were collected from four different manufacturers located in Texas and Wisconsin. Two replicates of the seven varieties of the cheeses were assigned to three temperatures (4, 13, and 22°C) and six storage periods (0,2,4, 8, 16, and 24 wk) in a 7 × 3 × 6 factorial arrangement. For all samples, indices of proteolysis were determined: the ratio of water-soluble N to total N and the ratio of 9.6% TCA-soluble N to total N. Hydrolysis and degradation of casein moieties of the cheeses during the 6-mo ripening were determined by PAGE pH and ADV were also determined. Percentages of water-soluble N in all cheese varieties were doubled after 2 wk of aging at 4°C. Soluble N (water-soluble N and TCA-soluble N) contents steadily increased as aging time and temperature increased for all cheeses, with some variations. pH, water-soluble N, and TCA-soluble N of soft cheeses were lower than those of hard varieties throughout the experimental period. The acid degree values were synergistically elevated by aging time and temperature, and those of the pepper soft cheese displayed extremely high values at 6 mo of aging. Effects of all three main factors (variety, time, and temperature) and their two-way and three-way interactions were significant for all proteolytic parameters tested. Correlations were positive among levels of water-soluble N, TCA-soluble N, and pH for all three temperature treatments. Electrophoretic degradation patterns of the protein samples exhibited a general positive relationship to levels of watersoluble N and TCA-soluble N in the corresponding cheeses at various aging treatments.

Estrogens do not affect whole-body protein metabolism in the prepubertal female.

The increase in bone mass, muscle bulk, and linear growth that occur during puberty are mediated, at least in part, through the action of sex steroids. By using infusions of nonradioactive tracers of leucine, we have recently shown a significant protein anabolic effect of testosterone in prepubertal boys. The present study was designed to determine whether estrogens can cause similar changes in protein metabolism in females. Seven prepubertal girls (Turner's syndrome, n = 6; hypogonadotropism, n = 1; mean age 12.2 +/- 0.3 yr) were studied. A 4-h infusion of L(-)[1-(13C)]leucine was given, and the isotopic enrichment of [13C]ketoisocaproic acid and 13CO2 were measured in plasma and in breath with use of gas chromatography/mass spectroscopy and an isotope ratio mass spectrometer, respectively. The reciprocal pool model was used for analysis of leucine kinetics. Subjects were then started on ethinyl estradiol orally (n = 5) or depot estradiol parenterally (n = 2). An identical study was repeated 4 weeks later. There were comparable changes in leucine kinetics in all girls studied, hence their data were grouped for analysis. After administration of ethinyl estradiol, there were insignificant changes in the rate of appearance of leucine, an index of proteolysis (+6% +/- 8%); leucine oxidation (-9% +/- 11%); and nonoxidative leucine disposal, an index of whole body protein synthesis (+10% +/- 8%). This is in sharp contrast to the changes found in boys studied similarly after treatment with testosterone (rate of appearance: 17 +/- 6%, P = .036; leucine oxidation -49 +/- 5%, P = 0.004; and nonoxidative leucine disposal +35 +/- 8%, P = 0.009). The lack of anabolic effect on whole-body protein in the girls reported here was observed despite significant increases in plasma insulin-like growth factor I concentrations during 4 h of sampling when comparing the 2 study days, similar to that of the prepubertal boys who were treated with testosterone. In summary, we observed that contrary to androgens, estrogens do not alter estimates of whole-body protein turnover and anabolism in prepubertal humans, despite significant increases in circulating insulin-like growth factor I concentrations. In conclusion, the impact of testosterone on protein metabolism seems to be a direct effect of androgens, independent of aromatization. These findings correlate with the significant differences in muscle bulk between the sexes as children go through puberty.

Proteolysis in Samples of Quarter Milk with Varying Somatic Cell Counts. 1. Comparison of Some Indicators of Endogenous Proteolysis in Milk

Eighty-six samples of quarter milk from 31 cows, the mean SCC of which exceeded 400,000 cells/ml, were analyzed for SCC, chloride content, pH, clotting time, total N, soluble N, casein N, proteose-peptone content, plasmin activity, and amount of free NH2 groups, parameters that are related to the udder health condition and to the deterioration of the protein quality. Analysis of the milk from each quarter separately improved the correlations considerably compared with analyses of samples from all 4 quarters mixed together. Measurement of free NH2 groups, using the 2, 4, 6-trinitrobenzene sulfonic acid, was not appropriate for estimating the extent of protein deterioration in milk samples with different SCC. Unlike SCC, the proteolysis index, plasmin activity, and the proteose-peptone content were highly correlated themselves and with most of the parameters related to proteolysis in milk. Proteolysis occurred in milk samples with SCC as low as 250,000 cells/ml. The quality of milk protein decreased unavoidably during lactation, regardless of SCC.

Myofibrillar protein synthesis in young and old human subjects after three months of resistance training

Muscle protein synthesis is slower in healthy older men and women than in young adults, but whether this results from relative disuse rather than aging is unclear. The present study was done to examine rates of myofibrillar protein synthesis before and after a 3-mo progressive resistance exercise program in young and old men and women. Protein synthesis was determined by incorporation of the tracer L-[1-13C]leucine into myofibrillar proteins obtained from the vastus lateralis muscle by needle biopsy. Before exercise, mean fractional myofibrillar synthesis was 33% slower (P < 0.01) in nine older subjects (62-72 yr old, 5 men and 4 women) than in 9 young subjects (22-31 yr old, 5 men and 4 women). Initial strength, as determined by three-repetition-maximum tests, was significantly less in the older group. Strength and training weights increased similarly in young and old groups, when expressed in relation to baseline values. Posttraining myofibrillar synthesis was determined on the day after the final training session. There was not a significant change in fractional myofibrillar synthesis in either the young or the old group after training, and the rate in the older group remained 27% slower (P < 0.05). Whole body protein turnover increased approximately 10% only in the younger group, and 24-h urinary 3-methylhistidine excretion (an index of myofibrillar proteolysis) was not significantly affected by training. These data suggest that the slower myofibrillar synthesis rate in older subjects cannot be explained by disuse.

Measurement of proteolysis in cheese: relationship between phosphotungstic acid-soluble N fraction by Kjeldahl and 2,4,6- trinitrobenzenesulphonic acid-reactive groups in water-soluble N

Free amino groups produced during cheese ripening are used to indicate the extent of cheese proteolysis. Several studies have shown a high correlation between the level of free amino acids and the flavour of Gouda (Aston et al. 1983) or Comté (Grappin &amp; Berdagué, 1989). Measurement of the level of free amino acids seems useful for the investigation of flavour chemistry in cheese (Lemieux et al. 1990). The determination of N fractions is often used to estimate the degree of proteolysis in cheese, but since this procedure is laborious and time consuming several attempts have been made to replace it by more rapid methods (Ardö &amp; Meisel, 1991). Since its introduction by Satake et al. (1960), the 2,4,6-trinitrobenzenesulphonic acid (TNBS) method has been widely used for the determination of free amino groups. Because TNBS does not react with the imino groups of histidine and proline or the hydroxyl groups of tyrosine, serine or threonine, it has been accepted as a selective reagent for primary amino groups (Burger, 1974). Measurement of N by Kjeldahl in the phosphotungstic acid (PTA)–sulphuric acid extract (Gripon et al. 1975) estimates the N of free amino acids and low molecular mass peptides. The purpose of this study was to compare the TNBS and PTA-soluble N methods in order to find out whether the TNBS procedure can replace that of PTA-soluble N in the determination of a cheese proteolysis index.

Ethanol Administration Alters the Proteolytic Activity of Hepatic Lysosomes

Protein accumulation in liver cells contributes to alcohol-induced hepatomegaly and is the result of an ethanol-elicited deceleration of protein catabolism (Alcohol Clin Exp Res 13:49, 1989). Because lysosomes are active in the degradation of most hepatic proteins, the present studies were conducted to determine whether ethanol administration altered the proteolytic activities of partially purified hepatic lysosomes. Rats were fed liquid diets containing either ethanol (36% of calories) or isocaloric maltodextrin for periods of 2-34 days. Prior to death, all animals were injected with [3H]leucine to label hepatic proteins. Rats subjected to even brief periods of ethanol feeding (2-8 days) exhibited significant hepatomegaly and hepatic protein accumulation compared with pair-fed control animals. Crude liver homogenates and isolated lysosomal-mitochondrial and cytosolic subfractions were incubated at 37 degrees C, and the acid-soluble radioactivity generated during incubation was measured as an index of proteolysis. At neutral pH, in vitro protein breakdown in incubated liver homogenates and subcellular fractions from control and ethanol-fed rats did not differ significantly. The extent of protein hydrolysis increased when samples were incubated at pH 5.5, which approximates the pH optimum for catalysis by lysosomal acid proteases. Under the latter conditions, partially purified lysosomes from control animals had 2-fold higher levels of proteolysis than corresponding fractions from ethanol-fed rats. The difference in proteolytic capacity appeared to be related to a lower latency and a higher degree of fragility of lysosomes from ethanol-fed rats at the acidic pH.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between cathepsin B activity and compositional parameters in dry-cured hams of normal and defective texture

Thirty-eight Italian dry-cured hams were analysed for cathepsin B activity, proximate composition and proteolysis index and results were related to lean tissue texture, as assessed by an expert panel, in order to search for relationships between excessive softness, a major problem in the raw ham industry, and chemical parameters. Softness was found to be related to protein breakdown which, in turn, was linked with higher residual cathepsin B activity and, to a lesser extent, to lower salt content. Results suggest that the use of raw ham of controlled enzyme activity would improve the texture quality of the end product.

Acute hyperglycemia enhances proteolysis in normal man.

The influence of hyperinsulinemic-hyperglycemia on protein and carbohydrate homeostasis was assessed using L-[1-13C]-leucine and [3-3H]glucose combined with open-circuit indirect calorimetry. After a 30-min basal period, healthy human volunteers were subjected to two sequential experimental periods (150 min each) during which insulin was continuously infused at a rate to elicit maximal effects (10.0 mU.kg-1 x min-1, resulting in 220-fold basal levels) in conjunction with an infusion of L-amino acids to maintain euleucinemia. Plasma glucose was maintained near basal (94 +/- 2 mg/dl) during period I and at twofold basal (191 +/- 4 mg/dl) during period II. The endogenous rate of leucine appearance (index of proteolysis in mumol.kg-1 x h-1) dropped by 80% from basal during period I (P < 0.01) but only by 44% during period II. Although hyperglycemia stimulated the rate of proteolysis threefold (18.0 +/- 10.2 to 49.8 +/- 7.2, P < 0.001), neither leucine oxidation nor nonoxidative leucine rate of disappearance (an estimate of protein synthesis) was altered. During both glycemic conditions, the rates of hepatic glucose production were completely suppressed, and this was accompanied by 3- and 11-fold increases in the estimated rates of protein and carbohydrate oxidation, respectively, and an 80% decrease in the rate of lipid oxidation. The estimated rate of glucose storage was increased fourfold during period I and by an additional 2.3-fold (to approximately 10-fold basal) in period II. The present study demonstrates that, during hyperinsulinemia, acute elevations of plasma glucose to two times basal levels result in a marked stimulation of whole body proteolysis during hyperinsulinemia.

Growth hormone acutely stimulates skeletal muscle but not whole-body protein synthesis in humans

In a previous study, a 6-hour local infusion of growth hormone (GH) into the brachial artery of normal subjects stimulated net muscle protein anabolism by augmenting skeletal muscle protein synthesis. In the present study, we examined whether systemically infused GH affects forearm and whole-body protein metabolism. Normal volunteers aged 18 to 24 years (n = 8) were given an 8-hour systemic infusion of 3H-phenylalanine and 14C-leucine. Between 90 and 120 minutes of tracer infusion, basal samples for determination of forearm and whole-body amino acid kinetics were taken. GH was then infused at 0.06 μg/kg/min, increasing GH concentration from 2.4 ± 0.3 to 32 ± 3 ng/mL. Systemic insulin-like growth factor 1 (IGF-1) level increased from 224 ± 20 to 262 ± 21 ng/mL (basal v 6-hour, P < .01). By 6 hours, GH suppressed forearm phenylalanine and leucine net release (each P < .05) by increasing 3H-phenylalanine (66%, P < .05) and 14C-leucine (13%, P < .05) extraction or disposal (R d). Whole-body leucine rate of appearance ([R a] an index of whole-body proteolysis) and nonoxidative leucine R d (whole-body protein synthesis) did not change over the course of the GH infusion, whereas oxidative leucine R d decreased (20%, P < .03). Acute stimulation of muscle but not whole-body protein synthesis by systemically infused GH suggests that muscle protein is acutely and specifically regulated by GH.

Monitoring Cheddar cheese ripening by chemical indices of proteolysis

Two Cheddar cheeses from two different production plants were ripened over 24 weeks at 10 degrees C and then analysed for peptides soluble in citrate buffer at pH 4.6 by reversed-phase (RP)-HPLC. Thirteen peptides with a chain length of between 35 and 65 amino acid residues and molecular masses between 3800 and 7400 were isolated and assigned to the corresponding amino acid sequences of the casein fractions via Edman degradation and amino acid composition. All peptides were fragments of the region K29-S96 of beta-casein A1 and A2, and eleven of them had M93 as the C-terminal. The amounts and proportions of these peptides varied differently during ripening of the two cheeses, so they may be suitable markers for characterizing the stage of ripening.

Richness of side-effects and poorness of analgesia from opiate in aimless pain

Muscle wasting impairs physical performance, increases mortality and reduces medical intervention efficacy in chronic diseases and cancer. Developing proficient intervention strategies requires improved understanding of the molecular mechanisms governing muscle mass wasting and recovery. Involvement of muscle protein- and myonuclear turnover during recovery from muscle atrophy has received limited attention. The insulin-like growth factor (IGF)-I signaling pathway has been implicated in muscle mass regulation. As glycogen synthase kinase 3 (GSK-3) is inhibited by IGF-I signaling, we hypothesized that muscle-specific GSK-3β deletion facilitates the recovery of disuse-atrophied skeletal muscle. Wild-type mice and mice lacking muscle GSK-3β (MGSK-3β KO) were subjected to a hindlimb suspension model of reversible disuse-induced muscle atrophy and followed during recovery. Indices of muscle mass, protein synthesis and proteolysis, and post-natal myogenesis which contribute to myonuclear accretion, were monitored during the reloading of atrophied muscle. Early muscle mass recovery occurred more rapidly in MGSK-3β KO muscle. Reloading-associated changes in muscle protein turnover were not affected by GSK-3β ablation. However, coherent effects were observed in the extent and kinetics of satellite cell activation, proliferation and myogenic differentiation observed during reloading, suggestive of increased myonuclear accretion in regenerating skeletal muscle lacking GSK-3β. This study demonstrates that muscle mass recovery and post-natal myogenesis from disuse-atrophy are accelerated in the absence of GSK-3β.

Aimless pain from idiopathic and pharmacological dysafferentation

Muscle wasting impairs physical performance, increases mortality and reduces medical intervention efficacy in chronic diseases and cancer. Developing proficient intervention strategies requires improved understanding of the molecular mechanisms governing muscle mass wasting and recovery. Involvement of muscle protein- and myonuclear turnover during recovery from muscle atrophy has received limited attention. The insulin-like growth factor (IGF)-I signaling pathway has been implicated in muscle mass regulation. As glycogen synthase kinase 3 (GSK-3) is inhibited by IGF-I signaling, we hypothesized that muscle-specific GSK-3β deletion facilitates the recovery of disuse-atrophied skeletal muscle. Wild-type mice and mice lacking muscle GSK-3β (MGSK-3β KO) were subjected to a hindlimb suspension model of reversible disuse-induced muscle atrophy and followed during recovery. Indices of muscle mass, protein synthesis and proteolysis, and post-natal myogenesis which contribute to myonuclear accretion, were monitored during the reloading of atrophied muscle. Early muscle mass recovery occurred more rapidly in MGSK-3β KO muscle. Reloading-associated changes in muscle protein turnover were not affected by GSK-3β ablation. However, coherent effects were observed in the extent and kinetics of satellite cell activation, proliferation and myogenic differentiation observed during reloading, suggestive of increased myonuclear accretion in regenerating skeletal muscle lacking GSK-3β. This study demonstrates that muscle mass recovery and post-natal myogenesis from disuse-atrophy are accelerated in the absence of GSK-3β.

Increased protein turnover in obese women

Some previous studies have indicated that rates of proteolysis and protein synthesis are greater in obese than in lean subjects, whereas others have not supported this finding. In the present study, we have measured postabsorptive protein turnover in a large group (n = 24) of obese women to establish more conclusively whether obese women have higher rates of protein turnover than lean women (n = 12), and to determine whether obese subjects with the greatest abdominal fat accumulation or those with the most severe insulin resistance (as determined by oral glucose tolerance testing) have the highest rates of protein turnover. Leucine appearance rate (R a) was used as an index of whole-body proteolysis, and the fraction of R a not oxidized was used as an index of whole-body protein synthesis. Leu R a, oxidation, and incorporation into protein after an overnight fast were approximately 25% greater in obese than in lean women, and were approximately 10% to 15% greater after dividing by lean body mass (LBM) or adjusting for LBM by analysis of covariance. Among obese women, the degree of obesity (over the range of 30% to 47% fat) was not a significant determinant of protein turnover, nor were degree of insulin resistance, visceral fat accumulation (determined by magnetic resonance imaging [MRI]), or subcutaneous abdominal fat accumulation (also determined by MRI). However, the women with the highest rates of protein turnover also had higher waist to hip circumference ratios (WHR). We conclude that even moderate obesity is associated with increased protein turnover, and that this effect is not completely explained by the higher LBM in obese subjects.

Monitoring Cheddar cheese ripening by chemical indices of proteolysis

The proteolysis of casein during cheese ripening was studied by reverse-phase (RP)-HPLC peptide mapping. Cheddar cheese from two different production plants were analysed during a 6-month ripening period at 4 o C and 10 o C. The elution profile obtained from cheese extracts soluble at pH 4.6 contained more than 120 peaks. These were grouped into four ranges of molecular mass (I 30 000 Da; III>10 000 Da; IV>3000 Da) by RP-HPLC of cheese extracts fractionated by ultrafiltration at different molecular mass cutoffs