Changes In Fructose Research Articles

The role of glucose and fructose on lipid droplet metabolism in human normal bronchial and cancer lung cells by Raman spectroscopy

Fructose is one of the most important monosaccharides in the human diet that the human body needs for proper metabolism. This paper presents an approach to study biochemical changes caused by sugars in human normal bronchial cells (BEpiC) and human cancer lung cells (A549) by Raman spectroscopy and Raman imaging. Results after supplementation of human bronchial and lung cells with fructose are also discussed and compared with results obtained for pure human bronchial and lung cells. Based on Raman techniques we have proved that peaks at 750 cm−1, 1126 cm−1, 1444 cm−1, 1584 cm−1 and 2845 cm−1 can be treated as biomarkers to monitor fructose changes in cells. Results for fructose have been compared with results for glucose. Raman analysis of the bands at 750 cm−1, 1126 cm−1, 1584 cm−1 and 2845 cm−1 for pure BEpiC and A549 cells and BEpiC and A549 after supplementation with fructose and glucose are higher after supplementation with fructose in comparison to glucose. The obtained results shed light on the uninvestigated influence of glucose and fructose on lipid droplet metabolism by Raman spectroscopy methods.

Assessment of Concentrated Liquid Coffee Acceptance during Storage: Sensory and Physicochemical Perspective.

Concentrated liquid coffees (CLCs) refer to stored extracts stable at environmental temperature, used as ingredients in the retail market. Their low chemical stability affects the sensory profile. This study was performed in two CLCs, one without additives (BIB) and another with a mix of sodium benzoate and potassium sorbate additives (SD), stored at 25 °C for one year. Quantitative-Descriptive (QDA) and discriminant analyses permitted identifying the critical sensory attributes and their evolution over time. The concentrate without additives presented an acceptance limit of 196 days (evaluated at a 50% acceptance ratio), while the additives increased the shelf life up to 226 days (38.9% improvement). The rejection was related to a decreased aroma, increased acidity, and reduced bitterness. A bootstrapped feature selection version of Partial Least Square analysis further demonstrated that reactions of 5-caffeoylquinic acid (5CQA) and 3,5-dicaffeoylquinic acid (3,5diCQA) could cause changes in the aroma at the first degradation stage. In the following stages, changes in fructose and stearic acid contents, a key indicator of acceptance for both extracts possibly related to non-enzymatic reactions involving fructose and other compounds, might affect the bitterness and acidity. These results provided valuable information to understand flavor degradation in CLCs.

Screening differentially expressed proteins of coronary heart disease with congenital cold syndrome based on tandem mass tag (TMT) technology

ABSTRACT In our previous studies, we discovered the congenital cold syndrome (CCS), which is characterized by ‘qi deficiency and qi stagnation, mixed cold and heat.’ And there is a type of syndrome with special incidence characteristic. However, the diagnosis of CCS still lacks an objective basis. In this study, we performed Tandem Mass Tag (TMT) based on quantitative proteomics technology to screen the significantly differentially expressed proteins (DEPs) in serum of patients with coronary heart disease (CHD) patients with CCS, patients with heart and kidney yang deficiency, and healthy people. A total of 22 DEPs (nine upregulated and 13 downregulated) were identified between patients with CCS and healthy subjects. Next, we performed GO and KEGG pathway enrichment analysis, we found the primary functions of DEPs of CCS were binding, catalytic activity, and molecular function regulator. These DEPs were mainly involved in important biological processes, such as cellular process, response to stimulus, localization, metabolic process, and biological regulation. The KEGG analysis revealed that the DEPs showed significant changes in fructose and mannose metabolism, Pentose phosphate pathway, and Arrhythmogenic right ventricular cardiomyopathy. After parallel reaction monitoring (PRM) verification, four upregulated target proteins (ALDOA, PCYOX1, Crisp3 and IGLV4-69) and three downregulated proteins (ALDOC, ADAMTSL-2 and C3) were accurately identified. These proteins were mainly related to immune response and glucose metabolism. These DEPs could be the marker proteins of coronary heart disease with CCS. This findings help to reveal the pathogenesis of CHD with CCS and provide potential therapeutic targets.

English

The effect of pasteurization-range heat treatment on yeast inactivation, vitamin C and the physicochemical characteristics of fresh pineapple juice were assessed. Yeast inactivation could be described by the Weibull model. The desired 6 log reduction was achieved at 63 and 65°C for 8 and 2 min, respectively. The pH, degree brix and organic acids did not change from 55 to 95°C. A significant change in fructose and glucose contents started to occur at 85°C, while sucrose hydrolysis was observed from 95°C. Likewise, hydroxymethylfurfural, one of the intermediate products of the Maillard reaction, was detected at 95°C.  Little degradation of ascorbic acid, the most important nutrient in pineapple juice- was observed. Hence, a mild heat treatment of 2 min at 65°C was sufficient to inactivate yeast and to preserve the nutritional and physicochemical quality of the pineapple juice.   Key words: Pineapple juice, heat treatment, yeast inactivation, physicochemical and nutritional quality.

Differences of sugar components in Different Mulberry Cultivars during its ripening

In this paper, seven mulberry varieties were used as experimental materials, and the composition and content of soluble sugar in different varieties of mulberry during its maturation process were analyzed by high performance liquid chromatography. The results showed that the changes of fructose and glucose content in different maturity of mulberry were basically the same during the ripening process, which reached the maximum in the color-changing period and slightly decreased in the mature period, among which the composition and content of soluble sugar in Taiwan long fruit mulberry were significantly different from other varieties; Fructose and glucose components were all detected in seven mulberry varieties, and only sucrose in Taiwan long-fruit mulberry varieties. This finding provides a scientific basis for the breeding of mulberry varieties and the study of sugar accumulation patterns of different varieties.

Distribution of organic metabolites after Fusarium wilt incidence in tomato (Solanum lycopersicum L.)

Tomato is an important vegetable crop worldwide and Fusarium wilt is a significant disease of tomato in many countries. One hundred and fifty three diverse tomato genotypes collected from local and exotic sources were screened for resistance to F. solani in the greenhouse. Significant variation in genotype response to inoculation was observed. The organic metabolite profiles of resistant and susceptible genotypes were assessed to determine the basis of resistance. Significant genetic variation was observed for ABA, malic acid, citric acid, fructose, glucose, sucrose, L-proline and myo-inositol. The disease treatment produced significant changes in fructose, glucose, proline and sucrose and significant genotype-by-treatment interaction was observed for ABA, citric acid, fructose, glucose, malic acid and sucrose, indicating that genetic improvement of these traits is feasible. Disease incidence was strongly associated with citric acid (R2 = 0.84), sucrose (R2 = 0.72) and L-proline (R2 = 0.76). Principal component analysis confirmed that citric acid and L-proline were important in determining plant disease response. Genetic variation for Fusarium wilt resistance can be used to develop new tomato cultivars with improved disease resistance.

Effects of divalent cations on the formation of 4(5)-methylimidazole in fructose/ammonium hydroxide caramel model reaction

The objective of the present study was to detail the changes of 4(5)-methylimidazole (4-MI) and its precursors in the presence of divalent cations (Ca2+, Mg2+) in a fructose/ammonium hydroxide caramel model system. The content of 4-MI and its precursor methylglyoxal (MGO) was inhibited by divalent cations (Ca2+, Mg2+). The possible explanation might be that fructose and its Heyns product glucosamine interact with divalent cations to form complexes and inhibit the degradation of glucosamine into MGO. Moreover, the changes of fructose, NH4+ and brown intensity in the presence of divalent cations indicated that fructose and glucosamine underwent intra-intermolecular polymerisation into melanoidins rather than the degradation reaction into aldehydes and ketones.

Reply to JS White

Dear Sir: Studies using dietary conditions with exaggerated nutritional compositions are often used to define the potential for biological responses and to act as starting points for understanding nutritional effects on health. The monkeys in the study consumed 30% more fructose than the unhealthiest humans, with fructose approximating the 95th percentile of total carbohydrate consumption (1, 2). This intake was modeled on the clinical study by Stanhope et al (3), which showed changes in adiposity, plasma lipids, and insulin sensitivity. Monkeys supplemented with fructose at this same amount (4) similarly experienced detrimental changes in these variables. Thus, our goal was to evaluate the influence of an extreme change in fructose while holding adiposity constant by careful focus on caloric and body weight control. One advantage of animal models, especially Old World monkeys with gastrointestinal tracts more comparable to humans, is sufficient longer-term environmental control to unmask perturbations induced by manipulation of nutritional variables. A potential next step would be to narrow the intake range over which health effects may be seen, while matching all dietary ingredients including protein source. Casein is known to be proatherogenic in the context of cholesterol-loaded dietary experiments (5); however, we actually reported no elevations in plasma or liver cholesterol concentrations (free or esterified) with high-fructose/casein diets, endpoints that are known risk factors for atherosclerosis (6). We therefore believe that the lack of differences seen in these endpoints in our study suggests that protein source did not primarily influence metabolic health, microbial translocation, and liver injury outcomes. We conclude that consumption of very high amounts of simple carbohydrate is likely to impair intestinal integrity and initiate liver and metabolic changes. Human and rodent studies involving exaggerated diets support the greater potency of fructose compared with glucose in initiation of such changes (3, 7), and future experiments should refine these findings using relevant diets in relevant animal studies.

Changes in the Volatile Compounds and Chemical and Physical Properties of Kuerle Fragrant Pear (Pyrus serotina Reld) during Storage

Volatiles from stored Kuerle fragrant pears (Pyrus serotina Reld) were studied using high-resolution gas chromatography and the solid-phase microextraction (SPME) method of gas chromatography/mass spectrometry (GC/MS). The dominant components were hexanal, ethyl hexanoate, ethyl butanoate, ethyl acetate, hexyl acetate, ethanol, alpha-farnesene, butyl acetate, and ethyl (E,Z)-2,4-decadienoate. By using GC-olfactometry, it demonstrated that the volatile compounds from SPME were responsible for the aroma of the Kuerle fragrant pear. The levels of sugars, organic acids, and phenolic acids in Kuerle fragrant pears were investigated using high-performance liquid chromatography (HPLC). Fructose was the dominant sugar, followed by glucose and sucrose. With increasing storage time, sucrose levels decreased; however, changes in fructose and glucose levels were not remarkable. There was a slight decrease in flesh firmness during storage. The general soluble solids concentration (SSC) declined slightly after 5 months storage. Some aroma-related volatile components increased during storage, while others decreased, especially the esters. The organic acids and phenolic acids also changed. The flavor of the Kuerle fragrant pears was affected by the change of volatile compounds and changes in chemical and physical properties.

Interactive effects of naphthalene treatment and the onset of vitellogenesis on energy metabolism in liver and gonad, and plasma steroid hormones of rainbow trout Oncorhynchus mykiss

The purpose of the study was to assess in female fish the possible interaction between treatment with a polycyclic aromatic hydrocarbon (PAH) like naphthalene and the onset of vitellogenesis. In a first experiment, female rainbow trout ( Oncorhynchus mykiss) at stages 2–3 (previtellogenesis) or 4 (early vitellogenesis) were intraperitoneally injected (2 μl g − 1 ) with vegetable oil alone (control) or containing naphthalene (50 mg kg − 1 ) to be sampled 3 h later. A second experiment was similarly designed but using fish intraperitoneally implanted (10 μl g − 1 ) with slow-release coconut oil implants alone (control) or containing 50 mg naphthalene kg − 1 body mass that were sampled 3 days after injection. On each sampling time, plasma levels of cortisol and 17β-estradiol, and several metabolic parameters in plasma, liver and gonad were assessed. In controls, early vitellogenic fish compared with previtellogenic fish displayed changes that in some cases are confirmatory of previous studies whereas in other cases provide new information in plasma (increased amino acid levels), liver (decreased capacity for exporting glucose and reduced amino acid levels) and gonad (decreased amino acid levels). Naphthalene treatment produced in previtellogenic fish decreased 17β-estradiol levels in plasma, increased plasma glucose or decreased liver gluconeogenic capacity whereas no major effects were noticed on parameters involved in lipid, amino acid and lactate metabolism. Differential effects of naphthalene treatment were noticed in early vitellogenic fish such as decreased 17β-estradiol and glucose levels in plasma, increased hexokinase and glucokinase and lack of changes in fructose 1,6-bisphosphatase activities in liver, and a lower decrease of amino acid levels in gonad. Those alterations produced by naphthalene treatment resulted in a decreased capacity for covering the energy demand of vitellogenesis in liver and gonad that could contribute to a delay and/or impairment of the onset of maturation.

Carbohydrate-Related Changes in Sweetpotato Storage Roots during Development

The quantity and pattern of carbohydrate-related changes during storage root development differed among six sweetpotato cultivars [Ipomoea batatas (L.) Poir. `Beauregard', `Heart-o-Gold', `Jewel', `Rojo Blanco', `Travis', and `White Star']. Measurements were taken for individual sugars, total sugars, alcohol-insoluble solids (AIS, crude starch), and dry weight (DW) at 2-week intervals from 7 to 19 weeks after transplanting (WAT) in two separate years. Sucrose was the major sugar during all stages of development, representing at least 68% of total sugars across all cultivars and dates. Pairwise comparisons showed `Heart-o-Gold' had the highest sucrose content among the cultivars. Sucrose content increased by 56% for `Heart-o-Gold' over the 12 weeks of assay, ranking first among the cultivars at 17 and 19 WAT and possessing 27% more sucrose than the next highest ranking cultivar, `Jewel', at 19 WAT. Fructose content profiles varied among and within cultivars. `Beauregard' showed a consistent increase in fructose throughout development while `Whitestar' showed a consistent decrease. The other cultivars were inconsistent in their fructose content profiles. Glucose content profiles were similar to those for fructose changes during development. The relationship between monosaccharides was fructose = 0.7207 × glucose + 0.0241. Cultivars with the highest fructose and glucose content could be selected by breeders after 13 WAT. Early clonal selection for high sucrose and total sugars is less promising because substantive changes in clonal rank occurred for sucrose and total sugars after 15 WAT. Cultivars ranking the highest in total sugars had either more monosaccharides to compensate for a lower sucrose content or more sucrose to compensate for a lower monosaccharide content. The relationship between DW and AIS was similar (AIS = 0.00089 × DW), and DW and AIS increased with time for most cultivars. Cultivars with high DW and AIS can be selected early during storage root development.

Changes in Fructose-Induced Production of Glucose in the Rat Liver Following Partial Hepatectomy

The fructose-induced production of glucose in the liver after partial hepatectomy (PH) was evaluated by using the liver-perfusion system. There was no significant difference in plasma glucose level between hepatectomized (HX) and sham-operated (SO) rats at 24 h after surgery, and, thereafter, almost similar levels were obtained in both groups. However, the level of serum free fatty acids (FFA) was significantly higher in HX rats than that in SO rats at 24 and 48 h after surgery. When both groups of rats were given fructose by gavage, the increment of plasma glucose was significantly larger in HX rats than in SO rats. Lactate infusion failed to increase the rate of glucose production in perfused livers of both HX and SO rats and there was no significant difference in the activity of hepatic phosphoenolpyruvate carboxykinase. By contrast, fructose infusion elicited a large increase in glucose production in the perfused livers of HX rats at 24 and 48 h after PH. The increase was closely associated with not the change in fructose 2,6-bisphosphate levels but the increment of the intracellular levels of citrate. Treatment of octanoate or oleate, which supplies acetyl-CoA via fatty acid oxidation, mimicked the fructose-induced increase in glucose production in SO rats with a concomitant increase in hepatic levels of citrate. These results suggest that the oxidation of FFA may play an important role in glucose production induced by fructose administration during the early phase of liver regeneration.

A Mechanism of Regulation of Hepatic Fru 2,6-P2Concentration upon Refeeding: Involvement of Xylulose 5-P and Cyclic-AMP

In order to determine the mechanism for delayed increase in Fructose 2,6-P2in livers of refed rats, the time course of changes in various metabolites upon refeeding NIH or high sucrose diet was investigated. Kinetics of increase in Fructose 2,6-P2and Xylulose 5-P were similar but different from hexose 6-P or glycogen in the livers of 48 h starved rats refed with NIH diet. The increase in the Fructose 2,6-P2level was a result of a combination of changes in Fructose 6-P,2-kinase and Fructose 2,6-bisphosphatase activity ratios, indicating dephosphorylation of the bifunctional enzyme and decreased cAMP. A similar correlation between Fructose 2,6-P2and Xylulose 5-P and dephosphorylation was observed with refeeding high sucrose diet and also with 16 h starved rats. These kinetic results are consistent with the idea that a specific protein phosphatase 2A, activated by Xylulose 5-P, dephosphorylates Fructose 6-P,2-kinase:Fructose 2,6-bisphosphatase and also decreased protein kinase A activity, resulting in increased hepatic Fructose 2,6-P2.

Carbohydrate content of Eucalyptus gunnii leaves along an annual cycle in the field and during induced frost-hardening in controlled conditions

The annual changes in frost hardiness were studied for three Eucalyptus gunnii genotypes. Frost resistance evaluated on leaf discs by the electrolyte leakage method reached a maximum in the coldest period and a minimum in summer demonstrating winter frost hardening. Genotype 634 exhibited a higher intrinsic resistance than the other genotypes both in the hardened and in the non-hardened stages. Plants of this genotype were also frost acclimated in controlled conditions by a progressive decrease of culture temperature (25 to 0 °C) but the degree of hardening appeared to be lower in these conditions. The carbohydrate patterns in leaves varied with acclimation. In controlled conditions the leaves of genotype 634 exhibited a rise in sucrose, fructose and raffinose concentration up to a temperature of 10 to 7 °C which subsequently decreased. In natural conditions a comparison of the three genotypes allowed us to correlate the higher intrinsic resistance of genotype 634 to a higher soluble sugar content. During acclimation fructose and raffinose changes were also correlated to an increase in cold resistance even though the kinetics of these changes differed in controlled and natural conditions. The starch content was very low in the various genotypes in the different conditions but oligosaccharides such as stachyose and possibly verbascose were detected. The results point out the relationships occurring between increased frost resistance and changes in fructose and raffinose concentration in E. gunnii leaves.

Role of fructose 2,6-bisphosphate in the control of heart glycolysis

The aim of this work was to study whether changes in fructose 2,6-bisphosphate concentration are correlated with variations of the glycolytic flux in the isolated working rat heart. Glycolysis was stimulated to different extents by increasing the concentration of glucose, increasing the workload, or by the addition of insulin. The glycolytic flux was measured by the rate of detritiation of [2-3H]- and [3-3H]glucose. Under all the conditions tested, an increase in fructose 2,6-bisphosphate content was observed. The glucose- or insulin-induced increase in fructose 2,6-bisphosphate content was related to an increase in the concentration of fructose 6-phosphate, the substrate of 6-phosphofructo-2-kinase. An increase in the workload correlated with a 50% decrease in the Km of 6-phosphofructo-2-kinase for fructose 6-phosphate. Similar changes in Km have been observed when purified heart 6-phosphofructo-2-kinase was phosphorylated in vitro by the cyclic AMP-dependent protein kinase or by the calcium/calmodulin-dependent protein kinase. Since the concentration of cyclic AMP was not affected by increasing the workload, it is possible that the change in Km of 6-phosphofructo-2-kinase, which was found in hearts submitted to a high load, resulted from phosphorylation by calcium/calmodulin protein kinase; other possibilities are not excluded. Anoxia decreased the external work developed by the heart, stimulated glycolysis and glycogenolysis, but did not increase fructose 2,6-bisphosphate.

Evidence for dissociation of gluconeogenesis stimulated by non-esterified fatty acids and changes in fructose 2,6-bisphosphate in cultured rat hepatocytes.

In order to examine the role of fructose 2,6-bisphosphate (Fru-2,6-P2) in non-esterified-fatty-acid-stimulated gluconeogenesis, Fru-2,6-P2 levels were measured in cultured rat hepatocytes under conditions mimicking the fasted state. After addition of either 1.5 mM-palmitate or 10 nM-glucagon, [U-14C]lactate incorporation into glucose increased 2-fold, but only glucagon suppressed Fru-2,6-P2. Prevention of palmitate oxidation with a carnitine palmitoyltransferase-I inhibitor (2-bromopalmitate) diminished glucose production and Fru-2,6-P2 levels. Addition of exogenous glucose to the media increased Fru-2,6-P2 in a dose-related manner, which was further augmented by addition of palmitate. When Fru-2,6-P2 levels were examined in cells cultured under conditions mimicking the fed state (significantly higher basal Fru-2,6-P2 levels and lower glucose production), palmitate oxidation was associated with a significant fall in Fru-2,6-P2. In conclusion, the present studies have demonstrated a dissociation between fatty-acid-stimulated gluconeogenesis and changes in Fru-2,6-P2 in cultured rat hepatocytes. Further experiments suggest that the accumulation of intracellular hexose 6-phosphate as a result of fatty-acid-stimulated gluconeogenesis masks a putative inhibitory effect of fatty acids on Fru-2,6-P2 concentrations.

POSTHARVEST STORAGE CONDITIONS INFLUENCE SUGAR LEVEL AND RATE OF CARBOHYDRATE CONVERSION DURING PUREEING OF SWEET POTATOES

Changes in fructose, sucrose, and glucose were investigated in cured roots of `Beauregard', `Jewel' and `Travis' sweet potatoes stored at 15°C and 1.5°C for 8 wk. Samples of 6 roots each in triplicate were analyzed at 2 wk intervals. At each interval, samples were also heated for 5, 10, 20 or 40 min. at 100°C to determine changes in rate of maltose conversion. Roots stored at 15°C displayed gradual or no increase in sugars over the 8 wk. Roots stored at 1.5°C increased more rapidly in sugars, especially fructose, over the same time. `Jewel' had the greatest increase in the sugars when stored at 1.5°C. There was no consistent pattern of maltose conversion in roots stored at 15°C over the 8 wk storage time. Roots stored at 1.5°C displayed a reduction in ability to convert starch to maltose upon heating. Less maltose was produced with increasing time of storag at 1.5°C. `Beauregard' and `Jewel' changed the most, while `Travis' changed only slightly.

Influence of Low Temperature on Respiration and Contents of Phosphorylated Intermediates in Darkened Barley Leaves

The aim of this work was to examine the effect of exposure of leaves to low temperatures (5 degrees C) upon the contents of phosphorylated intermediates and respiration in darkened barley (Hordeum vulgare L.) plants which differed in their carbohydrate status. In leaves that had previously been illuminated for 24 hours, there was a large increase in amounts of phosphorylated metabolites at 5 degrees C during the first 3 hours of darkness, compared with control plants kept at 30 degrees C. Hexose phosphates accounted for about two-thirds of this increase, which reached a peak after about 3 hours. At higher temperatures, there was a peak in the amount of fructose 2,6-bisphosphate and the rate of respiration which accompanied the transient increase in phosphorylated intermediates. At 5 degrees C the increase in phosphorylated intermediates was not accompanied by appreciable changes in fructose 2,6-bisphosphate, and there was a rapid decline in the rate of respiration. Leaves that had previously been darkened for 24 hours and that were low in carbohydrate failed to accumulate phosphorylated intermediates when exposed to low temperatures. The results are discussed with respect to the acclimation of carbohydrate metabolism to low temperatures. The results suggest that respiratory carbohydrate metabolism is strictly controlled even when the carbohydrate supply and glycolytic intermediates are abundant. The possibility that accumulation of hexose phosphates may be involved in acclimation of metabolism to low temperature is discussed.

Direct evidence that pyrophosphate: Fructose-6-phosphate phosphotransferase can act as a glycolytic enzyme in plants

Experiments were carried out to provide direct evidence that pyrophosphate: fructose-6-phosphate phosphotransferase (PFP) can operate as a glycolytic enzyme in some circumstances. A large increase in the rate of glycolysis was produced by adding uncoupler and alkalinising the medium of heterotrophic Chenopodium rubrum cells. Initially, a marked decrease in phospho enolpyruvate, 3-phosphoglycerate and hexose phosphates occurred, but no change in fructose 2,6-bisphosphate or inorganic pyrophosphate was observed. However, a gradual increase in the rate of O 2 uptake during the subsequent 5 min was accompanied by an increase in fructose 2,6-bisphosphate and a decrease in pyrophosphate, providing evidence that activation of PFP contributes to the increase in rate of glycolysis. This was accompanied by partial recovery of the adenine nucleotide energy status.

Fructose 2,6-bisphosphate and glucose 1,6-bisphosphate levels in erythrocytes with high and low 2,3-bisphosphoglycerate content during postnatal development

In rabbit and sheep erythrocytes the concentrations of 2,3-bisphosphoglycerate, fructose 2,6-bisphosphate and glucose 1,6-bisphosphate suffer important changes after birth, which differ in both species. The changes of fructose 2,6-bisphosphate and glucose 1,6-bisphosphate correlate with the changes in the levels of the enzymatic activities involved in their synthesis. The change of 2,3-bisphosphoglycerate levels in rabbit but not in sheep erythrocytes could be explained by the changes of the phosphofructokinase/pyruvate kinase and 2,3-bisphosphoglycerate synthase/2,3-bisphosphoglycerate phosphatase activity ratios.