The effect of starvation and starvation followed by feeding on enzyme activity and the metabolism of [U-14C]glucose in liver from growing chicks

1. The conversion of [U-(14)C]glucose into carbon dioxide, cholesterol and fatty acids in liver slices and the activities of ;malic' enzyme, citrate-cleavage enzyme, NADP-linked isocitrate dehydrogenase and hexose monophosphate-shunt dehydrogenases in the soluble fraction of homogenates of liver were measured in chicks that were starved or starved then fed. 2. In newly hatched chicks the incorporation of [U-(14)C]glucose and the activity of ;malic' enzyme did not increase unless the birds were fed. The response to feeding of [U-(14)C]glucose incorporation into fatty acids increased as the starved chicks grew older. 3. Citrate-cleavage enzyme activity increased slowly even when the newly hatched chicks were unfed. On feeding, citrate-cleavage enzyme activity increased at a much faster rate. 4. In normally fed 20-day-old chicks starvation decreased the incorporation of [U-(14)C]glucose into all three end products and depressed the activities of ;malic' enzyme and citrate-cleavage enzyme. Re-feeding increased all of these processes to normal or higher-than-normal levels. 5. In both newly hatched and 20-day-old chicks starvation increased the activity of isocitrate dehydrogenase and feeding or re-feeding decreased it. 6. Very little change in hexose monophosphate-shunt dehydrogenase activity was observed during the dietary manipulations. 7. The results indicate that increased substrate delivery to the liver is the principal stimulus to the increased rate of glucose metabolism observed in newly hatched chicks. The results also suggest that changes in the activities of ;malic' enzyme and citrate-cleavage enzyme are secondary to an increased flow of metabolites through the glucose-to-fatty acid pathway and that the dehydrogenases of the hexose monophosphate shunt play a minor role in NADPH production for fatty acid synthesis.     

The Glyoxylate Pathway in Acanthamoeba Sp.*

SYNOPSIS. Cell-free extracts of encysting Acanthamoeba were assayed for the key enzymes of the glyoxylate pathway, viz., isocitrate lyase and malate synthase. Both enzymes were present at the onset of encystment but their activities changed as cyst-wall formation proceeded to completion. Isocitrate lyase activity decreased during the first 4 hr of encystment to a minimum at 4 hr which was 70% of its initial activity. Activity then increased reaching a maximum at 9 hr which was 144% of its initial activity. After 9 hr a decrease in isocitrate lyase activity began which reached 70% of its initial activity at 35 hr. Malate synthase activity slowly decreased throughout encystment to 50% of its initial activity after 35 hr. From these data and others cited, it is concluded that this small soil amoeba has a functional glyoxylate pathway.     

Effects of haploidy and hybridization on the activities of four dehydrogenases in frog embryos

Total activities of four enzymes, malate dehydrogenase, lactate dehydrogenase, isocitrate dehydrogenase, and 6-phosphogluconate dehydrogenase were measured in diploid and androgenetic haploid embryos resulting from crosses of Rana pipiens pipiens and Rana pipiens sphenocephala. Developmental curves of these enzyme activities were compared with the DNA content of the embryos. The results suggest that decreased total enzyme activity in abnormal androgenetic haploid hybrids is due to the effects of reduced cellular proliferation and cellular degradation caused by a general nucleocytoplasmic incompatibility, not to the factors directly affecting the synthesis of each enzyme.     

Variation in Glyoxylate Bypass Inducibility among Strains of Tetrahymena pyriformis

SYNOPSIS. Seven strains of Tetrahymena pyriformis were assayed for log phase activity of the glyoxylate bypass enzymes isocitrate lyase and malate synthase. In strains 6I, 6II, 6III, and W, isocitrate lyase was induced; in HS, neither enzyme was induced by acetate. During growth in glucose- or acetate-containing media, strains 6III and GL had 2 periods of increased glyoxylate bypass and isocitrate dehydrogenase enzyme activities. Enzyme activities reached a maximum at the end of log phase, declined until the middle of stationary phase, and then increased again to a maximum near the end of stationary phase.     

Metabolic zonation in teleost gastrointestinal tract

Activities of several metabolic enzymes show distinct patterns of zonation along the intestinal tract of tilapia (Oreochromis niloticus), rainbow trout (Oncorhynchus mykiss) and copper rockfish (Sebastes caurinus). Zonation is species and enzyme specific, with different metabolic activities concentrated in specific areas, and few generalizations can be made. The rockfish show the smallest degree of zonation, with highest activities in the third quarter of the intestine, and shallow gradients to either side, and a general upswing in activity towards the distal end. In the trout, mitochondrial enzyme activities (citrate synthase, glutamate dehydrogenase, malate dehydrogenase) are highest in the pyloric caeca and decrease along the length of the small intestine. This pattern is accentuated for malic enzyme and glucose 6-phosphate dehydrogenase. These enzymes drop precipitously in activity after the first few sections of the small intestine, while other NADP-linked dehydrogenases (isocitrate dehydrogenase, and 6-phosphogluconate dehydrogenase) show moderate activity in pyloric caeca and peak toward the distal section of the small intestine. In tilapia, glutamate dehydrogenase shows a similar decrease as in trout, but citrate synthase peaks towards the distal sections. NADP-dependent dehydrogenases reveal distinct patterns, peaking in different sections of the intestine-malic enzyme in the proximal midsection, glucose 6-phosphate dehydrogenase in the distal mid-section, and isocitrate dehydrogenase in the anal section. Enzyme activities in the stomach of trout and tilapia also show zonation, with the midsection generally displaying the highest activities. A 5-day treatment of tilapia with an intraperitoneal cortisol deposit (25 mg kg(-1) wet mass) drastically alters metabolic performance along the gut in enzyme specific patterns, generally increasing enzyme activities in site-specific arrangements. Cortisol treatment also leads to the expected increases in activities of phosphoenolpyruvate carboxykinase, pyruvate kinase and aspartate aminotransferase in liver, but not in kidney. Aspartate aminotransferase is the only enzyme in brain significantly increased by cortisol treatment. Short-term food deprivation changes enzyme patterns, often resembling those observed after cortisol administration. We conclude that brain, liver and intestinal amino acid metabolism is an important target for cortisol action in fish and that metabolic zonation is a key factor to be reckoned with when analyzing physiological phenomena in the fish intestine.     

Developmental changes of lipogenic enzyme activities and lipogenesis in brown adipose tissue and liver of the rat.

1. Brown adipose tissue (BAT) and liver lipogenesis in vivo estimated by using 3H2O as tracer was very low and did not change significantly between 10 and 20 days after birth. Lipogenesis increased dramatically in both tissues by weaning at 20 days, peaking between 25 and 30 days of age. Since that time the rate of fatty acid synthesis in BAT decreased gradually to reach adult level after 2 months, whereas in the liver there was a sharp decrease of lipogenesis. 2. The activities of fatty acid synthase, citrate cleavage enzyme, malic enzyme and glucose 6-phosphate dehydrogenase essentially followed a similar course of developmental changes as lipogenesis. 3. In contrast to the enzymes listed above NADP-linked isocitrate dehydrogenase remained unaltered over the period studied, whereas lactate and malate dehydrogenases exhibited very high activity at 10 days after birth and from then decreased to reach adult level at the age of about 20 days. 4. The data obtained indicate that no substantial differences could be detected in the developmental pattern of lipogenesis and lipogenic enzyme activities between BAT and liver up to 30 days of age but after this time these processes were not co-ordinated in both tissues. Beyond this time the BAT was characterized by a much higher rate of lipogenesis than the liver. 5. The results are discussed in terms of the nutrient changes and the relationship between thermogenesis and lipogenesis in BAT.     

Changes in the activities of enzymes involved in amino acid metabolism during the senescence of detached wheat leaves

The activities of several enzymes related to amino acid metabolism were investigated in senescing detached wheat leaves ( Triticum aestivum L. cv. Diplomat) in light and darkness and after kinetin treatment. Glutamine synthetase and glutamate synthase activities rapidly declined in darkness. In light, the decline of glutamate synthase activity was retarded, while the activity of glutamine synthetase remained high and even increased transitorily. Kinetin treatment counteracted the decline of the activities of both enzymes. The activity of glutamate dehydrogenase markedly increased during senescence, particularly in light, and kinetin treatment lowered its activity. The activities of glutamate-oxaloacetate and glutamate-pyruvate amino-transferases and of NADP-dependent isocitrate dehydrogenase also increased in detached wheat leaves in light. Kinetin treatment prevented the rise of these enzyme activities. In darkness, the activities of glutamate-oxaloacetate aminotransferase and NADP-dependent isocitrate dehydrogenase decreased slowly while the decline of glutamate-pyruvate aminotransferase activity was more rapid. The activity of NAD-dependent malate dehydrogenase decreased both in light and, more rapidly, in darkness. The pattern of changes of the enzyme activities provides an explanation for the amino acid transformations and the flow of amino nitrogen into transport metabolites in senescing leaves.     

Effect of unsaturated fatty acids on the biosynthesis of glucose-repressed enzymes in yeast

In anaerobically glucose-grown yeast isocitrate lyase (EC 4.1.3.1.), malate synthase (EC 4.1.3.2.) and malate dehydrogenase (EC 1.1.1.37.) are repressed by glucose. 24 h cultures still contain 0.3–0.4% glucose in the medium, which is enough to completely repress these activities. Aeration of these cells, in buffer containing acetate, initiates the formation of the three enzymes. Within 16 h, the specific activities of these enzymes increase about 140, 120 and 70-fold, respectively. Glucose-6-phosphate dehydrogenase activity was not altered. When the yeast was grown anaerobically, but with a supplement of an unsaturated fatty acid in the medium, synthesis of the three enzymes was much faster and the specific activities after 16 h of derepression were considerably higher. A relationship exists between the number of double bonds in the unsaturated fatty acid molecule and its capability to stimulate enzyme synthesis: linolenic acid is more effective than linoleic acid, which, in turn, is much more effective than oleic acid. Increasing periods of aeration with glucose of anaerobically grown cells prior to derepression results in an increasing stimulation of enzyme synthesis on subsequent derepression. Anaerobic incubation of yeast in the presence of an unsaturated fatty acid in advance to derepression also increased the velocity of enzyme formation. It is suggested that during the aeration period with glucose and during anaerobic incubation with an unsaturated fatty acid a more active protein synthesizing apparatus was formed.     

Differential sensitivities to glucose and galactose repression of gluconeogenic and respiratory enzymes from Saccharomyces cerevisiae

The synthesis of isocitrate lyase was induced by the presence of ethanol in the chemostat reaching a specific activity of 200 mU·mg^-1 at this induced state. In glucoselimited, derepressed cells, 20 mU·mg^-1 were detected and under repressed conditions isocitrate lyase activity was not detected.The sensitivity of gluconeogenic enzymes: cytoplasmic malate dehydrogenase; fructose 1,6-bisphosphatase and isocitrate lyase as well as the mitochondrial enzymes NADH dehydrogenase and succinate cytochrome c oxidase to glucose and galactose repression were studied in chemostat cultures. Our results show that galactose was less effective as a repressor than glucose. Malate dehydrogenase was completely inactivated by glucose, whereas galactose only produced a 78% decrease of specific activity. Fructose 1,6-bisphosphatase and isocitrate lyase were completely inactivated by both sugars but at different rate. Glucose produced an 85% decrease of specific activity of the mitochondrial enzymes whereas galactose only decrease an 67%.     

Isocitrate Dehydrogenase and Glutamate Synthesis in Acetobacter suboxydans

Acetobacter suboxydans is an obligate aerobe for which an operative tricarboxylic acid cycle has not been demonstrated. Glutamate synthesis has been reported to occur by mechanisms other than those utilizing isocitrate dehydrogenase, a tricarboxylic acid cycle enzyme not previously detected in this organism. We have recovered alpha-ketoglutarate and glutamate from a system containing citrate, nicotinamide adenine dinucleotide (NAD), a divalent cation, pyridoxal phosphate, an amino donor, and dialyzed, cell-free extract. Aconitase activity was readily detected in these extracts, but isocitrate dehydrogenase activity, measured by NAD reduction, was masked by a cyanide-resistant, particulate, reduced NAD oxidase. Isocitrate dehydrogenase activity could be demonstrated after centrifuging the extracts at 150,000 x g for 3 hr and treating the supernatant fluid with 2-heptyl-4-hydroxyquinoline N-oxide. It is concluded that A. suboxydans can utilize the conventional tricarboxylic acid cycle enzymes to convert citrate to alpha-ketoglutarate which can then undergo a transamination to glutamate.     

The use of phenylmethylsulfonyl fluoride in the study of catabolite inactivation and repression in intact cells of Saccharomyces cerevisiae

Catabolite inactivation of fructose-1,6-bisphosphatase, isocitrate lyase, phosphoenolpruvate carboxykinase and malate dehydrogenase in intact cells could be prevented by phenylmethylsulfonyl fluoride added 40 min prior to the addition of glucose. Protein synthesis, fermentative and respiratory activity and catabolite repression were not affected. Elimination of catabolite inactivation by the addition of PMSF revealed that catabolite repression started at different times for different enzyme.Abbreviation PMSF phenylmethylsulfonyl fluoride     

Salt mediated changes in some enzymes of carbohydrate metabolism in halotolerantCladosporium sphaerospermum

Cladosporium sphaerospermum, isolated from salt pans was halotolerant. When grown in the presence of salt, the activities of invertase, isocitrate lyase, fructose-1,6 diphosphate aldolase and malate dehydrogenase were found to be increased and that of amylase decreased. Both, enzyme activation as well as an increase inde novo synthesis of enzymes were found to be some of the mechanisms of salt mediated changes. This may be one of the adaptive mechanisms, in halotolerantCladosporium sphaerospermum.     

Comparative Intermediary Metabolism of Vegetative Cells and Microcysts of Myxococcus xanthus

Crude extracts of both vegetative cells and glycerol-induced microcysts of Myxococcus xanthus contained the following enzyme activities: phosphofructokinase, phosphoglucoisomerase, fructose-1,6-diphosphatase, fructosediphosphate aldolase, glyceraldehyde-3-phosphate dehydrogenase, phosphopyruvate carboxylase, citrate synthase, isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, succinate dehydrogenase, malate dehydrogenase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, phosphoglucomutase, and uridine diphosphate glucose pyrophosphorylase. With the exception of isocitrate dehydrogenase, which was present at a fivefold higher concentration in microcysts, all activities in extracts from both types of cells were essentially equal. Hexokinase and pyruvate kinase could not be detected in extracts from either type of cell. Microcysts metabolized acetate at a lower rate than did vegetative cells. Most of this decrease was reflected in a substantial decrease in ability of microcysts to oxidize acetate to CO(2). In addition, microcysts and vegetative cells showed a different distribution of (14)C-label from incorporated acetate.     

不同浓度外源乙酸钠对耐乙酸大肠埃希菌DA19代谢和关键酶酶活的影响

为研究外源乙酸钠对大肠埃希菌DA19生长代谢的影响,将该菌株在氮源限制基本培养基及添加不同浓度乙酸钠的氮源限制基本培养基中连续培养,测定稳态时生长代谢参数和胞内关键酶酶活。与MN培养基相比,葡萄糖比消耗速率和延胡索酸比生成速率随外源乙酸钠质量浓度增加而逐渐下降,丙酮酸比生成速率则随外源乙酸钠质量浓度增加而明显增加,而乙酸比生成速率则明显降低(除9 g/L乙酸钠外)。磷酸果糖激酶、异柠檬酸脱氢酶、异柠檬酸裂解酶、苹果酸脱氢酶、磷酸烯醇式丙酮酸羧化酶和乙酸激酶酶活随外源乙酸钠质量浓度增加而呈先下降后上升的趋势,而6-磷酸葡萄糖脱氢酶则随着外源乙酸钠质量浓度增加而逐渐降低。为了应对外源乙酸钠压力,大肠埃希菌DA19的生长代谢和中心代谢途径酶活都发生了明显改变。     

Effects of controlled exposure of L cells to bromodeoxyuridine: II. Turnover rates and activity profiles during cell cycle of bromodeoxyuridine-sensitive and -resistant enzymes

Fluorodeoxyuridine (FUdR)-synchronized mouse L cells were allowed to incorporate 5-bromodeoxyuridine (BUdR) at restricted intervals in the S phase and the effects of the selective incorporation of BUdR in DNA on the activities of seven randomly chosen enzymes (five dehydrogenases and two phosphatases) were analysed. Reductions to 56.9 and 83.3 % of the control levels were noted for glucose-6-phosphate dehydrogenase (G6PD) and alcohol dehydrogenase (ADH) activities respectively, when cells were exposed to BUdR during the 1st h of S. Acid phosphatase (AcP) activity was reduced to 81.9% of the control level following exposure to the analogue during the 3rd h of S. Exposure of cells to BUdR for the entire S period failed to increase the magnitude of the reductions in activity for any of these three enzymes. Alternately, when cells were allowed to synthesize DNA in the presence of thymidine for the 1st h of S and the remainder in the presence of BUdR, the activities of G6PD and ADH were comparable to those found in untreated cells. Exposure of cells to thymidine for the 3rd h of S, combined with exposure to BUdR for the preceding and subsequent hours of S, provided complete protection against the BUdR-mediated reduction in AcP activity. The activities of lactate dehydrogenase (LDH), 6-phosphogluconate dehydrogenase (6pGD), isocitrate dehydrogenase (IDH) and alkaline phosphatase (A1P) were found to be insensitive to treatment with BUdR, even when the period of analogue exposure encompassed the entire S period.Additional investigations carried out with G6PD for characterization of the nature of the BUdR effects suggest that the BUdR-mediated reductions in enzyme activities are not caused by the increased rates of degradation of the enzymes, formation of enzyme inhibitors or by the disproportionate replication of A-T base pairs during BUdR treatment. The alterations of enzyme activities appear to result from decreased rates of synthesis of enzymes in BUdR-treated cells. The results of the present study clearly suggest that pulse labelling of cells with BUdR at various intervals of the S phase may provide a useful approach for determining temporal localization of replication time of DNA segments that are critical for the synthesis or regulation of specific gene products.     

Biochemical development of preimplantation mouse embryos: In vivo activities of fructose 1,6-diphosphate aldolase,glucose 6-phosphate dehydrogenase,malate dehydrogenase,and lactate dehydrogenase

The activities of four enzymes were determined during the first four days of mouse embryogenesis. Two enzymes, fructose 1,6-diphosphate aldolase and malate dehydrogenase, increase about 30% in activity, and this increase is attributed to slow but continued enzyme synthesis. The other two enzymes, glucose 6-phosphate dehydrogenase (X-linked) and lactate dehydrogenase, remain constant for the first two days and then decline exponentially with half-times of 19 and 17 hr, respectively. These declines in activity cannot be explained by the appearance of soluble inactivators or by the disappearance of soluble activators. Likewise, although temporally related to the passage of the embryos from the oviducts into the uterine horns, the changes in enzyme activity do not result from this change in embryonic environment, and specific degradative processes beginning on day 2 of embryonic development are postulated.This study was supported by USPHS Grant HD 03132 and by a grant from the School of Medicine, University of California, San Francisco Medical Center. The senior author is the recipient of USPHS Research Career Development Award HD 35,565.     

Enzyme histochemistry of the sheep uterus during the oestrous cycle

Enzyme histochemical techniques were applied to frozen sheep uteri from different stages of the oestrous cycle. The localization and activities of succinate, lactate, glucose-6-phosphate, and isocitrate (NADP+) dehydrogenases and acid and alkaline phosphatases were studied in the luminal and glandular epithelia, caruncle and myometrium. Enzyme activity in the sections was scored on a scale of 0--5. In general the enzyme activity in the uterine caruncles and epithelia was higher than in the myometrium. The myometrium did not show any alkaline phosphatase activity and isocitrate dehydrogenase (NADP+) activity was negligible. The low activities of acid phosphatase and lactate dehydrogenase and the moderate levels of glucose-6-phosphate and succinate dehydrogenases in the myometrium were constant. The caruncular tissue showed high levels of phosphatases and glucose-6-phosphate dehydrogenase, moderate levels of lactate and succinate dehydrogenases, and low levels of isocitrate dehydrogenase (NADP+) throughout the oestrous cycle. Much lower phosphatase and isocitrate dehydrogenase (NADP+) levels were found in the epithelium of deep glands compared with superficial glands. The high activity of acid and alkaline phosphatases in the luminal epithelium and the superficial glands was constant from mid-cycle to ovulation, but a significant decrease was observed immediately after ovulation. The level of dehydrogenases in epithelia was generally high and did not change during the oestrous cycle.     

Control of isocitrate lyase in Nocardia salmonicolor (NCIB9701).

Nocardia salmonicolor, grown on acetate, commercial D,L-lactate or hydrocarbon substrates, has high isocitrate lyase activities compared with those resulting from growth on other carbon sources. This presumably reflects the anaplerotic role of the glyoxylate cycle during growth on the former substrates. Amongst a variety of compounds tested, including glucose, pyruvate and tricarboxylic acid cycle intermediates, only succinate and fumarate prevented an increase in enzyme activity in the presence of acetate. When acetate (equimolar to the initial sugar concentration) was added to cultures growing on glucose, there followed de novo synthesis of isocitrated lyase and isocitrate dehydrogenase, with increases in growth rate and glucose utilization, and both acetate and glucose were metabolized simultaneously. A minute amount of acetate (40 muM) caused isocitrate lyase synthesis (a three-fold increase in activity within 3 min of addition) when added to glucose-limited continuous cultures, but even large amounts added to nitrogen-limited batch cultures were ineffective. Malonate, at a concentration that was not totally growth-inhibitory (1mM) prevented the inhibition of acetate-stimulated isocitrate lyase synthesis by succinate, but fumarate still inhibited in the presence of malonate. Phosphoenolpyruvate is a non-competitive inhibitor of the enzyme (apparent Ki 1-7 mM). The results are consistent with the induction of isocitrate or a closely related metabolite, and catabolite repression by a C-4 acid of the tricarboxylic acid cycle, possibly fumarate.     

TCA循环中间产物对酿酒酵母胞内代谢关键酶活性的影响

对酿酒酵母在添加苹果酸、柠檬酸和琥珀酸的混合培养基与其在YEPD培养基中胞内丙酮酸激酶、葡萄糖-6-磷酸脱氢酶、异柠檬酸脱氢酶、苹果酸脱氢酶、乙醇脱氢酶的酶活力差异进行了对比分析。结果表明:添加苹果酸使胞内丙酮酸激酶、异柠檬酸脱氢酶、苹果酸脱氢酶、乙醇脱氢酶的酶活分别下降34.82%、57.23%、39.15%、12.10%;添加柠檬酸使胞内丙酮酸激酶、异柠檬酸脱氢酶、苹果酸脱氢酶的酶活分别下降50.17%、42.20%、48.40%;添加琥珀酸使胞内丙酮酸激酶、葡萄糖-6-磷酸脱氢酶、异柠檬酸脱氢酶、苹果酸脱氢酶、乙醇脱氢酶的酶活分别下降34.16%、34.16%、50.87%、50.87%、12.37%。丙酮酸激酶、异柠檬酸脱氢酶和苹果酸脱氢酶对3种有机酸的耐受性较差,葡萄糖-6-磷酸脱氢酶、乙醇脱氢酶对3种有机酸的耐受具有选择性。     

Chemostat studies on the regulation of glucose metabolism in Pseudomonas aeruginosa by citrate

The effect of the relative concentrations of citrate and glucose on the regulation of key enzymes of the direct oxidative, phosphorylative, Entner-Doudoroff and pentose-cycle pathways of glucose metabolism in Pseudomonas aeruginosa has been investigated in continuous culture under conditions of NH(4) (+)-limitation. For comparison isocitrate dehydrogenase and aconitase were also assayed. Measurements were made for steady-state and transient conditions and the effect of growth rate was also studied. When cells grew on 75mm-citrate the glucose concentration had to attain 6-8mm before significant induction of enzymes of glucose metabolism occurred; the specific activities increased further as the result of both raising the glucose concentration to 30mm and then subsequently lowering the citrate to 60mm and then to 45mm. The specific activities of the glucose enzymes increased immediately during the transient period between the steady states characteristic of growth on 6mm- and 8mm-glucose, the increase continuing for about two doubling times. The converse experiment of adding increasing citrate concentrations to 45mm-glucose medium revealed an immediate induction of the citrate-transport system, oxidation of citrate following the increase in citrate concentration up to 8mm. Between 8mm- and 16mm-citrate a marked repression of gluconate, glucose 6-phosphate and 6-phosphogluconate dehydrogenases and the Entner-Doudoroff enzymes occurred. Increased growth rate in citrate medium resulted in decreased specific activities of glucose 6-phosphate dehydrogenase and isocitrate dehydrogenase. Increased growth rate in citrate-glucose medium gave decreased specific activities of isocitrate dehydrogenase and aconitase whereas the activities of some of the glucose enzymes decreased initially but then increased at the highest growth rate (0.5h(-1)), at which a marked increase in glucose utilization occurred. These observations accord with the regulation of glucose enzymes by induction with glucose or its metabolites and repression by citrate or its metabolic products.