Effect of anaerobiosis and anhydrobiosis on the extent of glycolytic enzyme binding in Artermia embryos

The effect of anaerobiosis and anhydrobiosis on the extent of binding of glycolytic enzymes to the particulate fraction of the cell was studied in Artemia salina embryos. During control aerobic development, trehalase, phosphofructokinase and pyruvate kinase showed an increase in the percentage associated with the particulate fraction which is consistent with the carbohydrate-based metabolism of Artemia embryos. However, anaerobiosis resulted in decreased enzyme binding for six glycolytic enzymes; hexokinase, aldolase, pyruvate kinase and lactate dehydrogenase were the exceptions. Decreased enzyme binding was also observed after exposure to dehydrating conditions. The results suggest that glycolytic rate could be regulated by changes in the distribution of glycolytic enzymes between free and bound forms in Artemia embryos. This reversible interaction of glycolytic enzymes with structural proteins may account for part of the metabolic arrest observed during anaerobic dormancy and anhydrobiosis.Abbreviation pH_i intracellular concentration of H⁺ ions     

Sucrose density gradient distribution of mitochondrial protein and enzymes from preclimacteric and climacteric pears

Mitochondrial fractions isolated from pears (Pyrus communis L.) at the climacteric minimum and peak were subjected to sucrose density gradient centrifugation. The distribution of protein and specific activities of 3 enzymes from this mitochondrial fraction were investigated.

Cytochrome oxidase specific activity remained associated with the particulate fraction and increased slightly during the period in which respiration of the whole fruit reached its climacteric peak. Catalase and acid phosphatase specific activity was associated with both the particulate and the least dense region of the gradient and decreased with postharvest ripening.

Evidence for several differences between the subcellular behavior of catalase and acid phosphatase from pear tissue compared to their counterparts isolated from mammalian cells is discussed. A general shift of maximum specific enzymic activities and protein distribution to lighter regions of the density gradient occurs with ripening, suggestive of diminution in size or density of intracellular particles.

     

Dependence of Wound-induced Respiration in Potato Slices on the Time-restricted Actinomycin-sensitive Biosynthesis of Phospholipid

Actinomycin D prevents the full development in a 24-hour period of both wound respiration and cyanide resistance only when given in the first 10 to 12 hours following the cutting of potato tuber (Solanum tuberosum var. Russet) slices. The capacity for choline incorporation into phosphatidylcholine increases with slice aging and is inhibited by actinomycin D in the same time-restricted way. The time-restricted effectiveness of actinomycin D applies to the cutting-elicited enhanced synthesis of three critical enzymes of phosphatidylcholine synthesis, namely phosphorylcholine-glyceride transferase, phosphorylcholine-cytidyl transferase, and phosphatidylphosphatase. By contrast, actinomycim D given at any time is without effect on the measurable levels after 24 hours of a selection of glycolytic and mitochondrial respiratory enzymes. Neither succinic dehydrogenase nor cytochrome oxidase activity increases with time in aging potato slices in the presence or absence of chloramphenicol. The foregoing observations emphasize the central role of phospholipid, and ultimately membrane biosynthesis, in the development of wound-induced respiration.     

Glycolytic enzyme binding and metabolic control in anaerobiosis

Summary Metabolic rate depression is a key survival strategy used by facultative anaerobes for enduring periods of environmental anoxia. In determining the molecular mechanisms of this phenomenon the role of enzyme binding to the subcellular particulate fraction was assessed in muscle tissues (ventricle and foot) of the anoxia tolerant marine gastropod,Busycotypus canaliculatum. Using two different methodologies for preparation, soluble versus particulate fractions of muscle were separated and assayed for their contents of eight glycolytic enzymes. Preparations from anoxic animals showed decreased percentages of enzymes associated with the particulate fraction as compared to controls; this was particularly pronounced for hexokinase and aldolase. A return to aerated seawater reversed this effect, and increased enzyme binding to the particulate fraction. The absence of a Pasteur effect in animal facultative anaerobes may be due, in part, to an anoxia-induced dissociation of enzymes from the particulate fraction of the cell promoting a decrease in glycolytic rate.Abbreviations HK hexokinase - PFK phosphofructokinase - GPDH glycerol-3-phosphate dehydrogenase - PK pyruvate kinase - LDH lactate dehydrogenase - ADH alanopine dehydrogenase - ODH octopine dehydrogenase - ALD aldolase - EDTA ethylenediamine tetraacetic acid - EGTA ethyleneglycol-bis-(2-amino ethylether)-N,N-tetraacetic acid     

Particulate and soluble forms of o-diphenol oxidase from potato tubers

A soluble and two different particulate forms of o-diphenol oxidase have been obtained from aged or fresh potato slices by differential and density gradient centrifugation. The particulate enzymes were shown to sediment with microsomes and peroxisomes, respectively. Over half the enzyme activity of aged slices was found to be particle bound, with approximately twice as much enzyme in the microsomes as in the peroxisomal fraction. Very similar distribution patterns have been obtained with fresh potatoes, which have an o-diphenol oxidase activity approximately one-third that of aged slices.     

Enzymes of glycerol metabolism in the storage tissues of Fatty seedlings

Various enzymes of glycerol metabolism in the extracts of 5-day-old eastor bean (Ricinus communis L. var. Hale) endosperm and 4-day-old peanut (Archis hypogaea L.) cotyledon were studied. NAD-glycerol dehydrogenase and NAD-α-glycerolphosphate dehydrogenase were not detected. Glycerol kinase was detected in the soluble fractions and an α-glycerolphosphate oxidoreductase was found in the particulate fractions. The particulate fractions were separated into various organelle fractions by sucrose gradient centrifugation and the α-glycerolphosphate oxidoreductase was shown to be present in the mitochondria. The properties of the castor bean mitochondrial α-glycerolphosphate oxidoreductase resembled those of a similar enzyme present in the mitochondria of many animal tissues. A survey showed that the α-glycerolphosphate oxidoreductase was present in great amount only in the storage tissues of fatty seedlings but not in other nonfatty plant tissues. It is concluded that in the storage tissues of fatty seedlings, the soluble glycerol kinase and the mitochondrial cytochrome-linked α-glycerolphosphate oxidoreductase are the two enzymes responsible for the initial conversion of glycerol to hexose.     

Subcellular localization of enzymes of anthocyanin biosynthesis in protoplasts

Flavanone synthase, chalcone-flavanone isomerase and UDP-glucose; anthocyanidin-3-O-glucosyltransferase activities of protoplasts and subcellular fractions of protoplasts of Hippeastrum and Tulipa were investigated. Subcellular fractions studied were intact vacuoles, cytosol and particulate components of protoplasts less the vacuole. The cytosol fraction had the highest activity of the three enzymes studied. Results similar to those found for Hippeastrum were obtained with fractions from leaves and petals of Tulipa. The increase in flavanone synthase activity in the cytosol fraction from petals of Hippeastrum during development paralleled the increase in anthocyanin content of the petals.     

Intracellular glucose and binding of hexokinase and phosphofructokinase to particulate fractions increase under hypoxia in heart of the amazonian armored catfish (Liposarcus pardalis)

Armored catfish (Liposarcus pardalis), indigenous to the Amazon basin, have hearts that are extremely tolerant of oxygen limitation. Here we test the hypothesis that resistance to hypoxia is associated with increases in binding of selected glycolytic enzymes to subcellular fractions. Preparations of isolated ventricular sheets were subjected to 2 h of either oxygenated or hypoxic (via nitrogen gassing) treatment during which time the muscle was stimulated to contract. The bathing medium contained 5 mM glucose and was maintained at 25 degrees C. Initial experiments revealed increases in anaerobic metabolism. There was no measurable decrease in glycogen level; however, hypoxic treatment led to a twofold increase in heart glucose and a 10-fold increase in lactate content. It is suggested that the increase in heart glucose content is a result of an enhanced rate of facilitated glucose transport that exceeds the rate of phosphorylation of glucose. Further experiments assessed activities of metabolic enzymes in crude homogenates and subsequently tracked the degree of enzyme binding associated with subcellular fractions. Total maximal activities of glycolytic enzymes (hexokinase [HK], phosphofructokinase [PFK], aldolase, pyruvate kinase, lactate dehydrogenase), and a mitochondrial marker, citrate synthase, were not altered with the hypoxic treatment. A substantial portion (>/=50%) of HK is permanently bound to mitochondria, and this level increases under hypoxia. The amount of HK that is bound to the mitochondrial fraction is at least fourfold higher in hearts of L. pardalis than in rat hearts. Hypoxia also resulted in increased binding of PFK to a particulate fraction, and the degree of binding is higher in hypoxia-tolerant fish than in hypoxia-sensitive mammalian hearts. Such binding may be associated with increased glycolytic flux rates through modulation of enzyme-specific kinetics. The binding of HK and PFK occurs before any significant decrease in glycogen level.     

Organization of the glycolytic enzymes in Escherichia coli

Differential centrifugation of osmotically lysed lysozyme-EDTA spheroplasts from Escherichia coli sedimented 50–70% of the glycolytic activities examined in a low speed pellet; the remaining activity, occurring in a high speed supernatant, contained the soluble enzymes of the cell. The distribution pattern of the enzymes could be altered by extrusion of the spheroplasts through the French Press or by lysis at different pH values. Electron micrographs of the pellet fraction revealed lysed spheroplasts mostly devoid of cellular constituents but consisting of cytoplasmic membranes surrounded by partially degraded cell wall fragments. Washing of the pellet showed that the enzymes were not all bound to the same degree to the membrane fraction. Throughput activity of the glycolytic pathway was demonstrated for the membrane fraction, but none was observed for the soluble fraction of the cell (i.e. for enzymes present in the supernatants) unless these were first concentrated by ultrafiltration. The supernatant from the lysed spheroplasts, together with a further supernatant obtained by washing the membrane pellet, was concentrated by ultrafiltration and chromatographed on a Bio-Gel column. The eluate contained glycolytic activities both in fractions corresponding to relatively high and relatively low molecular weight material The high molecular weight species, containing a proportion of all the enzymes studied, had a molecular weight of at least 1.2 × 10⁶. A multienzyme aggregate containing one each of the glycolytic enzymes would have a molecular weight of ～ 1.3 × 10⁶. The specific rate of pyruvate formation from glucose by the high molecular weight species was similar to that obtained from a preparation in which the fractions containing all the low molecular weight material enzyme activities were pooled and concentrated by ultrafiltration. Using the high molecular weight material, studies were made of the ability of added unlabelled glycolytic intermediates to compete for catalytic sites with intermediates produced endogenously from [¹⁴C₆] glucose. The relatively weak competition observed indicated a high degree of protection afforded the labelled intermediates derived from [¹⁴C₆] glucose.     

Membrane transformations in aging potato tuber slices

When potato tuber slices (Solanum tuberosum L.) are incubated with radioactive choline, labeled membrane-bound phospholipids are formed. If potato slices are aged for 0 to 24 hours before exposure to radioactive choline, the distribution of the labeled phospholipids undergoes both quantitative and qualitative changes. Quantitatively, there is a marked increase in the total lipoidal radioactivity with aging time. Qualitatively, there is a shift in the kinds of subcellular fractions that are being labeled. Fresh slices incorporate most of the lipoidal radioactivity in the microsomes. Slices aged for 9 hours incorporate most of the label in a fraction consisting of single membrane-bound cisternae, which are presumed to be dictyosomal fragments. Slices aged for 24 hours before incubation with radioactive choline incorporate the greater portion of the label in this same fraction, but a significant portion of the label is found in a heavier, mitochondria-containing fraction.     

Metabolic profile of wound-induced changes in primary carbon metabolism in sugarbeet root

Injury to plant products by harvest and postharvest operations induces respiration rate and increases the demand for respiratory substrates. Alterations in primary carbon metabolism are likely to support the elevated demand for respiratory substrates, although the nature of these alterations is unknown. To gain insight into the metabolic changes that occur to provide substrates for wound-induced increases in respiration, changes in the concentrations of compounds that are substrates, intermediates or cofactors in the respiratory pathway were determined in sugarbeet (Beta vulgaris L.) roots in the 4 days following injury. Both wounded and unwounded tissues of wounded roots were analyzed to provide information about localized and systemic changes that occur after wounding. In wounded tissue, respiration increased an average of 186%, fructose, glucose 6-phosphate, ADP and UDP concentrations increased, and fructose 1,6-bisphosphate, triose phosphate, citrate, isocitrate, succinate, ATP, UTP and NAD⁺ concentrations decreased. In the non-wounded tissue of wounded roots, respiration rate increased an average of 21%, glucose 6-phosphate, fructose 6-phosphate, glucose 1-phosphate and ADP concentrations increased, and isocitrate, UTP, NAD⁺, NADP⁺, and NADPH concentrations declined. Changes in respiration rate and metabolite concentrations indicated that localized and systemic changes in primary carbon metabolism occurred in response to injury. In wounded tissue, metabolite concentration changes suggested that activities of the early glycolytic enzymes, fructokinase, phosphofructokinase, phosphoglucose isomerase, and phosphoglucomutase were limiting carbon flow through glycolysis. These restrictions in the respiratory pathway, however, were likely overcome by use of metabolic bypasses that allowed carbon compounds to enter the pathway at glycolytic and tricarboxylic acid (TCA) cycle downstream locations. In non-wounded tissue of wounded roots, metabolic concentration changes suggested that glycolysis and the TCA cycle were generally capable of supporting the small systemic elevation in respiration rate. Although the mechanism by which respiration is regulated in wounded sugarbeet roots is unknown, localized and systemic elevations in respiration were positively associated with one or more indicators of cellular redox status.     

Characterization of arginase activity from mouse epidermis and its relation to ornithine decarboxylase induction by the tumor-promoting agent, 12-O-tetradecanoylphorbol-13-acetate

Arginase, which catalyzes the cleavage of l-arginine to urea and ornithine, was detected in both soluble and particulate fractions of mouse epidermis. In a typical experiment, about 75 and 25% of the total arginase activity was associated with the soluble (100 000 × g supernatant) and the washed particulate fraction, respectively. Both soluble and particulate enzymes required the presence of divalent Mn²⁺ for activity. Arginase activity was increased by about 50% in the particulate fraction, but not in the soluble fraction, by preheating the fractions at either 50 or 55°C in the presence of 15 mM MnCl₂. Enzyme activity in both fractions, in the absence of 15 mM MnCl₂, dropped precipitously during heating. A comparison of the nature of arginases in the soluble and particulate fractions revealed similar K_m values (13 mM) and pH optima (9.5) and identical heat denaturation curves. Application of 10 nmol of 12-O-tetradecanoylphorbol-13-acetate to mouse skin did not increase arginase activity in either fraction over a period of 24 h. In contrast, there was a large increase in ornithine decarboxylase activity in the soluble fraction 4.5 h after treatment. Mouse epidermal ornithine decarboxylase activity was much less than arginase activity and was predominantly localized in the soluble fraction. These results indicate that the normal level of arginase activity is not a limiting factor for the stimulation of polyamine biosynthesis by TPA. High arginase activity in mouse epidermis may play a role in providing ornithine for polyamine biosynthesis and in the production of glutamate and proline as well as in the production of keratinous proteins.     

Relative Contribution of Cytochrome-mediated and Cyanide-resistant Electron Transport in Fresh and Aged Potato Slices

The respiration of fresh potato (Solanum tuberosum, var. Russet Burbank) slices is predominantly cyanide-sensitive whether in the presence or absence of uncoupler. By contrast, the wound-induced respiration which develops in thin slices with aging is cyanide-resistant, and in the presence of cyanide, sensitive to chlorobenzhydroxamic acid, a selective inhibitor of the cyanide-resistant respiration. Titration of the alternate path in coupled slices with chlorobenzhydroxamic acid, in the presence and absence of cyanide, shows that the contribution of the cyanide-resistant pathway to the wound-induced respiration is zero. Similar titrations with uncoupled slices reveal that the alternate path is engaged and utilized extensively.

The maximal capacity of the cytochrome path (V_cyt) has been estimated in fresh and aged slices in the presence of the uncoupler carbonyl-cyanide m-chlorophenyl hydrazone. It has been found that V_cyt of aged slices is but 30 to 40% higher than that of fresh slices. The results suggest that the bulk of the wound-induced respiration is mediated through the cytochrome pathway which exists in fresh slices in suppressed form, and which is fully expressed by slice aging. The engagement of the alternate path by uncouplers in aged slices is attributed to an increase in substrate mobilization, with the result that the electron transport capacity of the cytochrome chain is exceeded.

     

Glutamate dehydrogenase from pumpkin cotyledons: characterization and isoenzymes

Glutamate dehydrogenase from pumpkin (Cucurbita moschata Pior. cultivar Dickinson Field) cotyledons was found in both soluble and particulate fractions with the bulk of the activity in the soluble fraction. Both enzymes used NAD(H) and NADP(H) but NAD(H) was favored. The enzymes were classified as glutamate-NAD oxidoreductase, deaminating (EC 1.4.1.3). Both enzymes were heat stable, had a pH optimum for reductive amination of 8.0, and were inhibited by high concentrations of NH₄⁺ or α-ketoglutarate. The soluble enzyme was more sensitive to NH₄⁺ inhibition and was activated by metal ions after ammonium sulfate fractionation while the solubilized particulate enzyme was not. Inhibition by ethylenediaminetetraacetate was restored by several divalent ions and inhibition by p-hydroxymercuribenzoate was reversed by glutathione. Particulate glutamate dehydrogenase showed a greater activity with NADP. The molecular weights of the enzymes are 250,000. Separation of the enzymes by disc gel electrophoresis showed that during germination the soluble isoenzymes increased from 1 to 7 in number, while only one particulate isoenzyme was found at any time. This particulate isoenzyme was identical with one of the soluble isoenzymes. A number of methods indicated that the soluble isoenzymes were not simply removed from the particulate fraction and that true isoenzymes were found.     

Respiratory Contribution of the Alternate Path during Various Stages of Ripening in Avocado and Banana Fruits

The respiration of fresh slices of preclimacteric avocado (Persea americana Mill. var. Hass) and banana (Musa cavendishii var. Valery) fruits is stimulated by cyanide and antimycin. The respiration is sensitive to m-chlorobenzhydroxamic acid in the presence of cyanide but much less so in the presence of antimycin. In the absence of cyanide the contribution of the cyanide-resistant pathway to the coupled preclimacteric respiration is zero. In uncoupled slices, by contrast, the alternate path is engaged and utilized fully in avocado, and extensively in banana. Midclimacteric and peak climacteric slices are also cyanide-resistant and, in the presence of cyanide, sensitive to m-chlorobenzhydroxamic acid. In the absence of uncoupler there is no contribution by the alternate path in either tissue. In uncoupled midclimacteric avocado slices the alternate path is fully engaged. Midclimacteric banana slices, however, do not respond to uncouplers, and the alternate path is not engaged. Avocado and banana slices at the climacteric peak neither respond to uncouplers nor utilize the alternate path in the presence or absence of uncoupler.

The maximal capacities of the cytochrome and alternate paths, V_cyt and V_alt, respectively, have been estimated in slices from preclimacteric and climacteric avocado fruit and found to remain unchanged. The total respiratory capacity in preclimacteric and climacteric slices exceeds the respiratory rise which attends fruit ripening. In banana V_alt decreases slightly with ripening.

The aging of thin preclimacteric avocado slices in moist air results in ripening with an accompanying climacteric rise. In this case the alternate path is fully engaged at the climacteric peak, and the respiration represents the total potential respiratory capacity present in preclimacteric tissue. The respiratory climacteric in intact avocado and banana fruits is cytochrome path-mediated, whereas the respiratory climacteric of ripened thin avocado slices comprises the alternate as well as the cytochrome path. The ripening of intact fruits is seemingly independent of the nature of the electron transport path.

Uncouplers are thought to stimulate glycolysis to the point where the glycolytic flux exceeds the oxidative capacity of the cytochrome path, with the result that the alternate path is engaged.

     

CELL STRUCTURE AND THE METABOLISM OF INSECT FLIGHT MUSCLE

The biochemical properties of insect flight muscle were investigated to ascertain the mechanisms whereby energy is made available for the contractile processes. It was found: 1. The endogenous respiration of muscle homogenates was diminished by starving the flies. The substrate for this respiration was probably glycogen. 2. To obtain the maximal rate of oxidation of glucose, the homogenate had to be fortified with inorganic phosphate, Mg ions, ATP, and cytochrome c. The nucleotides, AMP and ADP, were not as effective as ATP. The addition of DPN or TPN was not necessary for this system. 3. Flight muscle homogenates oxidized glycogen, some sugars, and amino acids, as well as the intermediates of the glycolytic and tricarboxylic acid cycles. Other evidence demonstrated the substrate specificity of the muscle. 4. By centrifugation, the muscle homogenate was divided into two fractions: one, a soluble fraction representing the sarcoplasm; the other, the particulate fraction which contained the fibrils and the sarcosomes. 5. The particulate fraction, alone, oxidized all the citric acid cycle intermediates, α-glycerophosphate, phosphopyruvate, and the amino acids, glutamic, proline, and cysteine. Regardless of the substrate, no oxygen uptake was found with the sarcoplasm by itself. 6. A recombination of the sarcoplasm and the particulate component was required for the oxidation of glycogen, the hexoses, and all the phosphorylated intermediates of glycolysis, except phosphopyruvate. 7. Isolated mitochondria accounted for all the enzymatic activity of the particulate fraction. These results demonstrate that the enzymes of intermediate metabolism are localized in the sarcoplasm or sarcosomes. The third cytological entity, the myofibrils, plays no role in the energy-providing scheme. From a functional viewpoint, the sarcoplasm and the mitochondria, in combination, furnish the energy for the actomyosin contraction. The results are discussed in relation to analogous findings in other insects and vertebrates.     

Activation of cPLA2, PKC, and ERKs in the Rat Cerebral Cortex During Ischemia/Reperfusion

Release of the excitotoxic amino acid, glutamate, into the extracellular space during ischemia/reperfusion contributes to neuronal injury and death. To gain insights into the signal transduction pathways involved in glutamate release we examined the time course of changes in enzyme levels and activities of cPLA₂, PKC and ERKs in the rat cerebral cortex after four vessel (4VO) ischemia followed by reperfusion. Measurement both by enzymatic assay and Western blot analysis showed significant increases in the activity and protein levels of cPLA₂ during 10–20 min of ischemia. Activity remained elevated at 10 min and 20 min of reperfusion, whereas cPLA levels had returned to base line levels after 20 min of reperfusion. PKC activity increased significantly in the particulate, but not in the cytosolic, fractions both during ischemia and reperfusion. Increases in PKC levels were recorded in the particulate fraction during ischemia and reperfusion, and in the cytosolic fraction during ischemia. Western blot analysis with a phosphospecific antibody for characterization of MAPK (ERKs) activation revealed significantly increased phosphorylation of ERK₁, and ERK₂ in the particulate fraction, of ERK₂ in the cytosolic fraction, during ischemia and of both enzymes in the particulate and cytosolic fractions after 10 min of reperfusion. The relevance of the results to glutamate release is discussed.     

Effects of cortisone, starvation, and rickets on oxidative enzyme activities of epiphyseal cartilage from rats

Epiphyseal cartilage fractions from rats have been shown to have the enzymatic complement for oxidizing a wide variety of substrates though at relatively low rates compared to tissues such as liver and heart. In contrast to previous data for glycolytic enzymes, mitochondrial oxidative enzyme levels do not appear to be specifically affected by dietary rickets, starvation, or cortisone treatment and do not correlate with the oxidative activity of cartilage slices. These findings give added emphasis to our earlier suggestion that control of glycolytic enzyme levels plays a central role in regulation of cartilage cell economy.A marked difference in the relative distribution between supernatant and pellet fractions of glycerol-3-P oxidase compared to other typical mitochondrial enzymes including succinate dehydrogenase is interpreted as evidence for two classes of mitochondria in cartilage. According to this hypothesis, there is a class of more readily sedimented mitochondria which contain relatively much more glycerol-3-P oxidase. Although this enzyme is thought to play a role in regulation of glycolysis, the control of synthetic-degradative mechanisms for it does not appear to be coordinated with those for the glycolytic enzymes and glycerol-3-P dehydrogenase of the cartilage cytoplasm. It is suggested that the oxidase may have a special role in Ca²⁺ accumulation by mitochondria.     

Effect of auxin on the metabolism of mevalonic acid in suspension-cultured carrot cells

The rate of incorporation of [¹⁴C]mevalonate into carotenoid and steroid fractions in suspension-cultured carrot cells decreased markedly after 2,4-dichlorophenoxyacetic acid was removed from the medium. In parallel to this change, the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase in a microsomal fraction was reduced to ca 33% of the control value, while that of a particulate fraction showed no significant change. The activities of mevalonate activating enzymes remained unchanged after auxin deprivation.     

Evidence for glycolytic enzyme binding during anaerobiosis of the foot muscle ofPatella caerulea (L.)

Summary The effect of anaerobiosis and aerobic recovery on the degree of binding of glycolytic enzymes to the particulate fraction of the cell was studied in the foot muscle of the marine molluscP. caerulea, in order to assess the role of glycolytic enzyme binding in the metabolic transition between aerobic and anoxic states. Short periods of anoxia (2 h, 4 h) resulted in an increase in enzyme binding in association with the increased glycolytic rate observed; this was particularly pronounced for phosphorylase, phosphofructokinase, aldolase, pyruvate kinase and lactate dehydrogenase. Decreased enzyme binding was observed after prolonged periods of anoxia. These effects were reversed and control values re-established when animals were returned to aerobic conditions. The results suggest that glycolytic rate could be regulated by changes in the distribution of glycolytic enzymes between free and bound forms inP. caerulea foot muscle. This reversible interaction of glycolytic enzymes with structural proteins may constitute an additional mechanism for metabolic control.