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1.
When a buffered, aerobic suspension of ethanol-grown cells of Saccharomyces cerevisiae is treated with ethanol, a rapid flux of metabolism is observed from endogenous phosphoenolpyruvate to hexose monophosphates. Intracellular concentrations of phosphoenolpyruvate, 2-phosphoglycerate, and 3-phosphoglycerate record a monotonic drop, while those of triose phosphates and fructose 1,6-diphosphate fall after an early rise; fructose 6-phosphate, mannose 6-phosphate, and glucose 6-phosphate levels rise to a plateau. Prior growth on glucose extinguishes fructose 1,6-diphosphatase activity and completely arrests the rise of the hexose monophosphates. By using mutants blocked at a number of glycolytic steps it has been concluded that the metabolic flow takes place along the Embden-Meyerhof pathway in the reverse direction bypassing pyruvate kinase and fructose 6-phosphate kinase. Ethanol acts as a trigger by supplying NADH at the glyceraldehyde 3-phosphate dehydrogenase step. The rate of the reversal in the span phosphoenolpyruvate to fructose 1,6-diphosphate approaches 40 μ mol of 3-carbon units per minute per gram of wet cells. The in vivo activity of fructose 1,6-diphosphatase is nearly a quarter of this rate. 相似文献
2.
The photosynthetic carbon reduction cycle intermediates can be divided into three classes according to their effects on the rate of photosynthetic CO 2 evolution by whole spinach ( Spinacia oleracea) chloroplasts and on their ability to affect reversal of certain inhibitors (nigericin, arsenate, arsenite, iodoacetate, antimycin A) of photosynthesis: class I (maximal): fructose 1, 6-diphosphate, dihydroxyacetone phosphate, glyceraldehyde-3-phosphate, ribose-5-phosphate; class 2 (slight): glucose 6-phosphate, fructose 6-phosphate, ribulose-1, 5-diphosphate; class 3 (variable): glycerate 3-phosphate. While class 1 compounds influence the photosynthetic rate, they do not lower the Michaelis constant of the chloroplast for bicarbonate or affect strongly other photosynthetic properties such as the isotopic distribution pattern. It was concluded that the class 1 compounds influence the chloroplast by not only supplying components to the carbon cycle but also by activating or stabilizing a structural component of the chloroplast. 相似文献
3.
1. The orthophosphate inhibition of photosynthesis by isolated spinach chloroplasts can be reversed by 3-phosphoglycerate, dihydroxyacetone phosphate, glyceraldehyde 3-phosphate, fructose 6-phosphate and fructose 1,6-diphosphate. 2. Metabolically related compounds such as ribulose 1,5-diphosphate, glucose 6-phosphate, 6-phosphogluconate and phosphoenolpyruvate are ineffective. 3. The kinetics of reversal are characteristic of the intermediate used, but, in each instance, the onset of oxygen evolution is accompanied by a carbon dioxide fixation and except with 3-phosphoglycerate the stoicheiometry is close to unity. 4. The nature of orthophosphate inhibition and its reversal is discussed in relation to metabolic control of photosynthesis. 相似文献
4.
Several metabolites, including those of glycolysis, the citric acid cycle, the hexose monophosphate shunt, glutamate, aspartate, and Coenzyme A were measured in defined parietal cell-enriched freeze-dried sections of dog gastric biopsies derived from nonsecreting and secreting tissue. In addition, NH3, ribulose 5-phosphate, glycerol, and succinate were measured in perchloric acid extracts of biopsies. The onset of secretion increased the level of glycolytic intermediates including pyruvate and lactate with the most marked increase being in fructose 1,6-diphosphate levels. The level of 6-phosphogluconate and ribulose 5-phosphate also increased, in spite of a constant NADP+/NADPH ratio. The levels of all the citric acid cycle intermediates measured also rose, the most marked rise being in malate and fumarate. The levels of glycerol, acetyl-CoA, and CoA increased, but the ratio of the latter intermediates remained constant. Calculation of the ratio of the oxidized to reduced form of diphosphopyridine nucleotide indicated a fall of the ratio in the cytoplasm and a rise in the mitochondria. From these data, it is concluded that the major energy source for acid secretion is due to an increase in citric acid cycle activity and that glycolysis, and probably also fatty acid oxidation, is stimulated to provide mitochondrial substrate. 相似文献
5.
CO 2 fixation by a suspension of isolated spinach chloroplasts was terminated by turning off the light, and changes of metabolite levels in the chloroplast stroma and the surrounding medium were assayed. Whereas CO 2 fixation comes to a total stop within 15 seconds, a conversion of triose phosphates to heptose, hexose, and pentose monophosphates is found to occur for 1 to 2 minutes afterwards. It seems from these data that an inactivation of fructose and sedoheptulose bisphosphatases proceeds with a lag period. In contrast, the conversion of pentose monophosphates to ribulose 1,5-bisphosphate is inhibited immediately after the stop of illumination. As the stromal level of freely available ATP was not depleted under this condition, these data demonstrate that ribulose 5-phosphate kinase was very rapidly inactivated after darkening of the chloroplasts. Essentially, the same effect is also observed when CO 2 fixation is partially inhibited by addition of moderate concentrations of m-chlorocarbonyl phenylhydrazone, partially uncoupling photophosphorylation. It appears from these results, that the activity of ribulose 5-phosphate kinase is not only regulated by light through the mediation of reduced carriers like thioredoxin but also by alternative parameters, e.g. stromal metabolite levels. 相似文献
6.
The stimulation or inhibition of ribulose diphosphate oxygenase by a variety of compounds is compared with the reported effects on these compounds on the ribulose diphosphate carboxylase activity. A possible transition state analog of ribulose diphosphate, 2-carboxyribitol 1, 5-diphosphate, at a molar ratio of inhibitor to enzyme of 10 to 1, irreversibly inactivates the oxygenase and carboxylase activities. This is consistent with the hypothesis that there may be a single active site for both the carboxylase and oxygenase activities. Several compounds of the reductive pentose photosynthetic carbon cycle act as effectors of the ribulose diphosphate oxygenase in a manner complementary to their reported effect upon the carboxylase. Ribose 5-phosphate inhibits the oxygenase with an apparent Ki of 1.8 mM, but it is reported to activate the carboxylase; fructose 6-phosphate and glucose 6-phosphate act similarly but are less effective than ribose 5-phosphate. Fructose 1. 6-diphosphate stimulates the oxygenase at low magnesium ion concentrations. The stimulatory effect of 6-phosphogluconate on the oxygenase is associated with a 3-fold reduction of the Km (Mg2+). ATP inhibits the oxygenase but has been reported to stimulate the carboxylase; pyrophosphate acts in an opposite manner. From these results it appears that the ratio of carboxylase to oxygenase activity may be a variable factor with predictable subsequent alteration in the ratio between photosynthetic CO2 fixation and photorespiration. 相似文献
7.
Glucose 6-phosphate, fructose 6-phosphate, fructose 1, 6-diphosphate, and triose phosphates, and the enzymes phosphofructokinase, aldolase, and glucose 6-phosphate dehydrogenase were extracted from banana fruit ( Musa cavendishii, Lambert var. Valery) at the ( a) preclimacteric, ( b) climacteric rise, ( c) climacteric peak, and ( d) postclimacteric stages of ripening. The level of fructose 1, 6-diphosphate increased 20-fold whereas the concentration of other intermediates changed no more than 2.5-fold between stages a and c. For these same extracts, phosphofructokinase activity increased 2.5-fold whereas the activity of glucose 6-phosphate dehydrogenase and aldolase changed only fractionally. Substrate saturation studies (fructose 6-phosphate) of phosphofructokinase activity showed a decrease in the [S] 0.5 from 5.6 to 1.7 mM betwen stages a and c. The enzyme from both sources seems to be regulated by a negative cooperative effect with the control being more stringent in the enzyme from stage a. The difference in enzyme activity is consistent with the increase in respiratory activity between the two stages. 相似文献
8.
A model of the C
3 photosynthetic system is developed which describes the sensitivity of the steadystate rate of carbon dioxide assimilation to changes in the activity of several enzymes of the system. The model requires measurements of the steady-state rate of carbon dioxide assimilation, the concentrations of several intermediates in the photosynthetic system, and the concentration of the active site of ribulose 1,5-bisphosphate carboxyalse/oxygenase (Rubisco). It is shown that in sunflowers ( Helianthus annuus L.) at photon flux densities that are largely saturating for the rate of photosynthesis, the steady-stete rate of carbon dioxide assimilation is most sensitive to Rubisco activity and, to a lesser degree, to the activities of the stromal fructose, 6-bisphosphatase and the enzymes catalysing sucrose synthesis. The activities of sedoheptulose 1,7-bisphosphatase, ribulose 5-phosphate kinase, ATP synthase and the ADP-glucose pyrophosphorylase are calculated to have a negligible effect on the flux under the high-light conditions. The utility of this analysis in developing simpler models of photosynthesis is also discussed.Abbreviations
c
i
intercellular CO 2 concentration
-
C
infP
supJ
control coefficient for enzyme P with respect to flux J
- DHAP
dihydroxyacetonephosphate
- E4P
erythrose 4-phosphate
- F6P
fructose 6-phosphate
- FBP
fructose 1,6-bisphosphate
- FBPase
fructose 1,6-bisphosphatase
- G3P
glyceraldehyde 3-phosphate
- G1P
glucose 1-phosphate
- G6P
glucose 6-phosphate
- Pi
inorganic phosphate
- PCR
photosynthetic carbon reduction
- PGA
3-phosphoglyceric acid
- PPFD
photosynthetically active photon flux density
-
R
n
J
response coefficient for effector n with respect to flux J
- R5P
ribose 5-phosphate
- Rubisco
ribulose 1,5-bisphosphate carboxylase/oxygenase
- Ru5P
ribulose 5-phosphate
- RuBP
ribulose 1,5-bisphosphate
- S7P
sedoheptulose 7-phosphate
- SBP
sedoheptulose 1,7-bisphosphate
- SBPase
sedoheptulose 1,7-bisphosphatase
- SPS
sucrose-phosphate synthase
- Xu5P
xylulose 5-phosphate
-
n
P
elasticity coefficient for effector n with respect to the catalytic velocity of enzyme P
This research was funded by an Australian Research Council grant to I.E.W. and was undertaken during a visity by K.A.M. to the James Cook University of North Queensland. The expert help of Glenys Hanley and Mick Kelly is greatly appreciated. 相似文献
9.
1. The dissimilation of a number of externally added hexose phosphates and 5′-nucleotides by the perfused rat heart is described, and non-specific esterase and 5′-nucleotidase activity associated with the superficial cell membrane or vascular system has been demonstrated. 2. The rate of production of 14CO 2 from [U- 14C]glucose 6-phosphate suggests that oxidation occurred after hydrolysis to glucose. The incorporation of isotope from [U- 14C]glucose 6-phosphate into glycogen was small, and similar to that obtained with [U- 14C]glucose as substrate. 3. Glucose 6-phosphate was also partially isomerized to fructose 6-phosphate. Similarly, fructose 6-phosphate was converted mainly into glucose 6-phosphate, but also into glucose and inorganic phosphate. When fructose 1,6-diphosphate was added to the perfusate, a mixture of glucose 6-phosphate, fructose 6-phosphate and triose phosphates accumulated in the medium approximately in the equilibrium proportions of the phosphohexose-isomerase and triose phosphate-isomerase reactions, together with inorganic phosphate and some glucose. Glucose 1-phosphate was hydrolysed to glucose, but was not converted into glucose 6-phosphate. Leakage of enzymes out into the perfusion fluid did not occur. 4. This demonstration that phosphohexose isomerase, triose phosphate isomerase and aldolase may react with extracellular substrates at an appreciable rate suggests that these enzymes are attached to the cell membrane. 相似文献
10.
1. The maximum catalytic activities of fructose diphosphatase from flight muscles of bumble-bees (Bombus spp.) are at least 30-fold those reported for the enzyme from other tissues. The maximum activity of fructose diphosphatase in the flight muscle of any particular bee is similar to that of phosphofructokinase in the same muscle, and the activity of hexokinase is similar to or greater than the activity of phosphofructokinase. There is no detectable activity of glucose 6-phosphatase and only a very low activity of glucose 6-phosphate dehydrogenase in these muscles. The activities of both fructose diphosphatase and phosphofructokinase vary inversely with the body weight of the bee, whereas that of hexokinase is relatively constant. 2. There is no significant hydrolysis of fructose 1-phosphate, fructose 6-phosphate, glucose 1,6-diphosphate and glycerol 3-phosphate by extracts of bumble-bee flight muscle. 3. Fructose 1,6-diphosphatase from bumble-bee flight muscle and from other muscles is inhibited by Mn(2+) and univalent cations; the potency of inhibition by the latter varies in the order Li(+)>Na(+)>K(+). However, the fructose diphosphatase from bumble-bee flight muscle is different from the enzyme from other tissues in that it is not inhibited by AMP. 4. The contents of ATP, hexose monophosphates, fructose diphosphate and triose phosphates in bumble-bee flight muscle showed no significant changes between rest and flight. 5. It is proposed that both fructose diphosphatase and phosphofructokinase are simultaneously active and catalyse a cycle between fructose 6-phosphate and fructose diphosphate in resting bumble-bee flight muscle. Such a cycle would produce continuous hydrolysis of ATP, with the release of energy as heat, which would help to maintain the thoracic temperature during rest periods at a level adequate for flight. 相似文献
11.
Two novel procedures have been used to regulate, in vivo, the formation of phosphoenolpyruvate (PEP) from glycolysis in Streptococcus lactis ML3. In the first procedure, glucose metabolism was specifically inhibited by p-chloromercuribenzoate. Autoradiographic and enzymatic analyses showed that the cells contained glucose 6-phosphate, fructose 6-phosphate, fructose-1,6-diphosphate, and triose phosphates.Dithiothreitol reversed the p-chloromercuribenzoate inhibition, and these intermediates were rapidly and quantitatively transformed into 3- and 2-phosphoglycerates plus PEP. The three intermediates were not further metabolized and constituted the intracellular PEP potential. The second procedure simply involved starvation of the organisms. The starved cells were devoid of glucose 6-phosphate, fructose 6-phosphate, fructose- 1,6-diphosphate, and triose phosphates but contained high levels of 3- and 2-phosphoglycerates and PEP (ca. 40 mM in total). The capacity to regulate PEP formation in vivo permitted the characterization of glucose and lactose phosphotransferase systems in physiologically intact cells. Evidence has been obtained for "feed forward" activation of pyruvate kinase in vivo by phosphorylated intermediates formed before the glyceraldehyde-3-phosphate dehydrogenase reaction in the glycolytic sequence. The data suggest that pyruvate kinase (an allosteric enzyme) plays a key role in the regulation of glycolysis and phosphotransferase system functions in S. lactis ML3. 相似文献
12.
1. Purified rabbit-muscle and -liver glucose phosphate isomerase, free of contaminating enzyme activities that could interfere with the assay procedures, were tested for inhibition by fructose, fructose 1-phosphate and fructose 1,6-diphosphate. 2. Fructose 1-phosphate and fructose 1,6-diphosphate are both competitive with fructose 6-phosphate in the enzymic reaction, the apparent Ki values being 1·37×10 −3−1·67×10 −3m for fructose 1-phosphate and 7·2×10 −3−7·9×10 −3m for fructose 1,6-diphosphate; fructose and inorganic phosphate were without effect. 3. The apparent Km values for both liver and muscle enzymes at pH7·4 and 30° were 1·11×10 −4−1·29×10 −4m for fructose 6-phosphate, determined under the conditions in this paper. 4. In the reverse reaction, fructose, fructose 1-phosphate and fructose 1,6-diphosphate did not significantly inhibit the conversion of glucose 6-phosphate into fructose 6-phosphate. 5. The apparent Km values for glucose 6-phosphate were in the range 5·6×10 −4−8·5×10 −4m. 6. The competitive inhibition of hepatic glucose phosphate isomerase by fructose 1-phosphate is discussed in relation to the mechanism of fructose-induced hypoglycaemia in hereditary fructose intolerance. 相似文献
13.
Low concentrations of hydrogen peroxide strongly inhibit CO 2 fixation of isolated intact chloroplasts (50% inhibition at 10 −5 M hydrogen peroxide). Addition of catalase to a suspension of intact chloroplasts stimulates CO 2 fixation 2–6 fold, indicating that this process is partially inhibited by endogenous hydrogen peroxide formed in a Mehler reaction. The rate of CO2 fixation is strongly increased by addition of Calvin cycle intermediates if the catalase activity of the preparation is low. However, at high catalase activity addition of Calvin cycle intermediates remains without effect. Obviously the hydrogen peroxide formed at low catalase activity leads to a loss of Calvin cycle substrates which reduces the rate of CO2 fixation. 3-Phosphoglycerate-dependent O2-evolution is not influenced by hydrogen peroxide at a concentration (5 · 10−4 M) which inhibits CO2 fixation almost completely. Therefore the inhibition site of hydrogen peroxide cannot be at the step of 3-phosphoglycerate reduction. Dark CO2 fixation of lysed chloroplasts in a hypotonic medium is not or only slightly inhibited by hydrogen peroxide (2.5 · 10−4 M), if ribulose-1,5-diphosphate, ribose 5-phosphate or xylulose 5-phosphate were added as substrates. However, there is a strong inhibition of CO2 fixation by hydrogen peroxide, if fructose 6-phosphate together with triose phosphate are used as substrates. This indicates that hydrogen peroxide interrupts the Calvin cycle at the transketolase step, leading to a reduced supply of the CO2-acceptor ribulose 1,5-diphosphate. 相似文献
14.
2′-Deoxyribonucleosides are important as building blocks for the synthesis of antisense drugs, antiviral nucleosides, and 2′-deoxyribonucleotides for polymerase chain reaction. The microbial production of 2′-deoxyribonucleosides from simple materials, glucose, acetaldehyde, and a nucleobase, through the reverse reactions of 2′-deoxyribonucleoside degradation and the glycolytic pathway, was investigated. The glycolytic pathway of baker’s yeast yielded fructose 1,6-diphosphate from glucose using the energy of adenosine 5′-triphosphate generated from adenosine 5′-monophosphate through alcoholic fermentation with the yeast. Fructose 1,6-diphosphate was further transformed to 2-deoxyribose 5-phosphate in the presence of acetaldehyde by deoxyriboaldolase-expressing Escherichia coli cells via d-glyceraldehyde 3-phosphate. E. coli transformants expressing phosphopentomutase and nucleoside phosphorylase produced 2′-deoxyribonucleosides from 2-deoxyribose 5-phosphate and a nucleobase via 2-deoxyribose 1-phosphate through the reverse reactions of 2′-deoxyribonucleoside degradation. Coupling of the glycolytic pathway and deoxyriboaldolase-catalyzing reaction efficiently supplied 2-deoxyribose 5-phosphate, which is a key intermediate for 2′-deoxyribonucleoside synthesis. 2′-Deoxyinosine (9.9 mM) was produced from glucose, acetaldehyde, and adenine through three-step reactions via fructose 1,6-diphosphate and then 2-deoxyribose 5-phosphate, the molar yield as to glucose being 17.8%. 相似文献
15.
1. Carbon dioxide fixation by isolated pea chloroplasts was stimulated by the addition of intermediates of the Calvin photosynthesis cycle and by some related compounds. 2. Ribose 5-phosphate and fructose 1,6-diphosphate consistently produced the largest effects; free sugars such as erythrose and sedoheptulose and acids such as glycollate and glyoxylate were largely ineffective or even inhibitory. 3. Small effects were produced by fructose and ribose but not by their isomers, glucose and xylose. 4. Maximal rates in the presence of ribose 5-phosphate varied between 10 and 50μmoles of carbon dioxide fixed/mg. of chlorophyll/hr. 相似文献
16.
alpha-Glycerophosphate dehydrogenase (EC 1.1.99.5) in mitochondria from liver of the triiodothyronine-treated rats is competitively inhibited by phosphoenolpyruvate, glyceraldehyde 3-phosphate and 3-phosphoglycerate, the apparent Ki values for phosphoenolpyruvate being 0.76 mM at pH 7.0, 1.7 mM at pH 7.4 and 3.5 mM at pH 7.7. The apparent Ki values for glyceraldehyde 3-phosphate and 3-phosphoglycerate are also pH-dependent. Other glycolytic intermediates, such as 2-phosphoglycerate, 2,3-diphosphoglycerate, pyruvate, glucose 6-phosphate, fructose 6-phosphate and fructose 1,6-diphosphate did not alter significantly alpha-glycerophosphate dehydrogenase activity. Palmitoyl-CoA is a competitive inhibitor of this enzyme, with Ki value of about 30 micron. 相似文献
17.
2-Deoxyribose 5-phosphate production through coupling of the alcoholic fermentation system of baker's yeast and deoxyriboaldolase-expressing Escherichia coli was investigated. In this process, baker's yeast generates fructose 1,6-diphosphate from glucose and inorganic phosphate, and then the E. coli convert the fructose 1,6-diphosphate into 2-deoxyribose 5-phosphate via D-glyceraldehyde 3-phosphate. Under the optimized conditions with toluene-treated yeast cells, 356 mM (121 g/l) fructose 1,6-diphosphate was produced from 1,111 mM glucose and 750 mM potassium phosphate buffer (pH 6.4) with a catalytic amount of AMP, and the reaction supernatant containing the fructose 1,6-diphosphate was used directly as substrate for 2-deoxyribose 5-phosphate production with the E. coli cells. With 178 mM enzymatically prepared fructose 1,6-diphosphate and 400 mM acetaldehyde as substrates, 246 mM (52.6 g/l) 2-deoxyribose 5-phosphate was produced. The molar yield of 2-deoxyribose 5-phosphate as to glucose through the total two step reaction was 22.1%. The 2-deoxyribose 5-phosphate produced was converted to 2-deoxyribose with a molar yield of 85% through endogenous or exogenous phosphatase activity. 相似文献
18.
The levels of glucose, sugar phosphates, and adenosine phosphates were determined in primary leaves of intact bean plants during normal senescence and compared to leaves in which senescence was delayed by application of benzyladenine (BA). In both cases there was a rise with time in the levels of glucose 1-phosphate, glucose 6-phosphate, and fructose 6-phosphate, and a decline in 2-phosphoglyceric acid, inorganic phosphate, and the adenosine phosphates (AMP, ADP, ATP). The levels of fructose 1,6-diphosphate remained fairly constant. Although the levels of hexose phosphates, adenosine phosphates, and inorganic phosphate were lower in the BA-treated leaves, the incorporation of 32P into these compounds by 3- and 6-week-old plants was higher than in the controls. These results suggest that the retardation of leaf senescence by BA in intact bean plants is associated with increased utilization of metabolites, indicating a more rapid turnover of the adenosine phosphates. It is concluded that this effect is brought about by a regulatory coordination of metabolic processes in relation to energy production and utilization. 相似文献
19.
The behavior of mammalian phosphofructokinase on immobilized adenine nucleotides was investigated. Three different insolubilized ligands were compared using a pure rabbit muscle phosphofructokinase. N6-[(6-aminohexyl)-carbamoyl-methyl]-ATP-Sepharose bound at least 90 times more enzyme than either N6-(6-aminohexyl)-AMP-agarose or ATP-adipic acid hydrazide-Sepharose. The elution of phosphofructokinase from the ATP-Sepharose with various metabolites and combinations of metabolites was investigated. The enzyme is eluted specifically from N6-[(6-aminohexyl)-carbamoyl]-ATP-Sepharose with a mixture of 25 μm each of fructose 6-phosphate and ADP (±Mg 2+). The enzyme is not eluted either with ATP (25 μm), fructose 1,6-diphosphate (1 mm), ADP (25 μm), fructose 6-phosphate (1 mm) alone, or with a mixture of fructose 1,6-diphosphate (25 μm) and ATP (25 μm). The recovery of bound enzyme was usually greater than 90%. A mixture of glucose 6-phosphate and ADP or a mixture of IDP and fructose 6-phosphate also elutes the enzyme, but the recovery with these eluants was only about 40%. It was concluded that the “dead-end” complex is the most effective in the elution. Using this method, phosphofructokinase has been prepared in an essentially homogeneous form from muscle and brain of rabbit and rat. The overall isolation procedure involves a high speed centrifugation of crude extracts which sediments phosphofructokinase as a pellet, followed with adsorption on N6-[(6-aminohexyl)-carbamoyl-methyl]-ATP-Sepharose and specific elution with the mixture of fructose 6-phosphate and ADP. 相似文献
20.
1. Ox sternomandibularis muscle was ;slow-frozen' by placing it in air at -22 degrees or ;fast-frozen' by immersion in liquid air or acetone-solid carbon dioxide. In all cases muscles were frozen pre-rigor. Changes in length, pH and the concentrations of P(i), creatine phosphate, hexose monophosphate (glucose 1-phosphate+glucose 6-phosphate+fructose 6-phosphate), fructose diphosphate (fructose 1,6-diphosphate+(1/2) triose phosphate), lactate, ATP, ADP, AMP and NAD(+) during freezing and during subsequent thawing were determined. In addition some measurements were made of the changes in alpha-glycerophosphate, 3-phosphoglycerate, 2-phosphoglycerate, phosphoenolpyruvate and pyruvate concentrations during slow freezing. 2. Appreciable shortening and marked changes in chemical composition took place during slow freezing but not during fast freezing. 3. During slow freezing the hexose monophosphate concentration fell and fructose 1,6-diphosphate and triose phosphate increased substantially. Increases also took place in 3-phosphoglycerate, 2-phosphoglycerate and phosphoenolpyruvate, but not in pyruvate. 4. On thawing, most of the chemical changes were similar to those in unfrozen muscle post mortem, but took place much more rapidly; loss of NAD(+) was particularly rapid. Fast-frozen muscle metabolized at a faster rate on thawing than did slow-frozen muscle. 5. The overall changes in length during freezing and thawing were about the same in slow-frozen as in fast-frozen muscle. 相似文献
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