Effect of glucose and fructose on food intake via malonyl-CoA signaling in the brain

In the brain malonyl-CoA serves the important function of monitoring and modulating energy balance. Because of its central role in the metabolism of higher animals, glucose acts as the principal indicator of global energy status. Specialized neuronal nuclei within the hypothalamus sense blood glucose and signal higher brain centers to adjust feeding behavior and energy expenditure accordingly. As the level of glucose entering the brain rises, food intake is suppressed. Energy status information triggered by glucose is transmitted via hypothalamic signaling intermediaries, i.e. AMPK and malonyl-CoA, to the orexigenic/anorexigenic neuropeptide system that determines hunger and energy expenditure. The central metabolism of glucose by the glycolytic pathway generates ATP which produces a compensatory decrease in AMP level and AMPK activity. Since acetyl-CoA carboxylase (ACC) is a substrate of AMPK, lowering AMP increases the catalytic activity of ACC and thereby, the level of its reaction product, malonyl-CoA. Malonyl-CoA signals the anorexigenic-orexigenic neuropeptide system to suppress food intake. Unlike glucose, however, centrally metabolized fructose increases food intake. This paradox results because fructose bypasses the rate-limiting step of glycolysis and uses a rapid ATP-requiring reaction that abruptly depletes ATP and provokes a compensatory rise in AMP. Thus, fructose has the opposite effect of glucose on the AMPK/malonyl-CoA signaling system and thereby, feeding behavior. The fact that fructose metabolism by the brain increases food intake and obesity risk raises health concerns in view of the large and increasing per capita consumption of high fructose sweeteners, especially by youth.     

Adenine nucleotide degradation during energy depletion in human lymphoblasts. Adenosine accumulation and adenylate energy charge correlation.

Adenine nucleotide breakdown to nucleosides and purine bases was measured in cultures of human lymphoblastoid cells following: 1) the inhibition of oxidative phosphorylation in the absence of glucose or 2) the addition of 2-deoxyglucose. A mutant cell line, deficient in adenosine kinase, in the presence of an adenosine deaminase inhibitor was used to measure utilization of the two pathways of AMP catabolism involving initial action of either purine 5'-nucleotidase or AMP deaminase. In such a system the appearance of adenosine induced by the oxidative phosphorylation inhibitor, rotenone, implies that approximately 70% of AMP breakdown occurs via dephosphorylation. By the same method, deamination accounts for 82% of AMP breakdown when 2-deoxyglucose is added. The occurrence of AMP dephosphorylation is not correlated with elevated concentrations of substrate or with decreased concentrations of the inhibitors of 5'-nucleotidase, ATP and ADP. Dephosphorylation occurs if, and only if, the adenylate energy charge decreases to about 0.6 in these experiments. In cultures deprived of glucose and oxygen, adenine nucleotide degradation via dephosphorylation results in recovery of normal energy charge values.     

The Effect of Adenine Nucleotides on Purified Phosphoenolpyruvate Carboxylase from the CAM Plant Crassula argentea

The effects of adenine nucleotides on phosphoenolypyruvate carboxylase were investigated using purified enzyme from the CAM plant, Crassula argentea. At 1 millimolar total concentration and with limiting phosphoenolpyruvate, AMP had a stimulatory effect, lowering the K_m for phosphoenolpyruvate, ADP caused less stimulation, and ATP decreased the activity by increasing the K_m for phosphoenolpyruvate. Activation by AMP was not additive to the stimulation by glucose 6-phosphate. Furthermore, AMP increased the K_a for glucose 6-phosphate. Inhibition by ATP was competitive with phosphoenolpyruvate. In support of the kinetic data, fluorescence binding studies indicated that ATP had a stronger effect than AMP on phosphoenolpyruvate binding, while AMP was more efficient in reducing glucose 6-phosphate binding. As free Mg²⁺ was held constant and saturating, these effects cannot be ascribed to Mg²⁺ chelation. Accordingly, the enzyme response to the adenylate energy charge was basically of the “R” type (involving enzymes of ATP regenerating sequences) according to D. E. Atkinson's (1968 Biochemistry 7: 4030-4034) concept of energy charge regulation. The effect of energy charge was abolished by 1 millimolar glucose 6-phosphate. Levels of glucose 6-phosphate and of other putative regulatory compounds of phosphoenolpyruvate carboxylase were determined in total leaf extracts during a day-night cycle. The level of glucose 6-phosphate rose at night and dropped sharply during the day. Such a decrease in glucose 6-phosphate concentration could permit an increased control of phosphoenolpyruvate carboxylase by energy charge during the day.     

Relating Cerebral Ischemia and Hypoxia to Insult Intensity

The contributions of five variables believed to influence the brain's metabolism of O2 during hypoxia [duration, PaO2, delta CMRO2 (the difference between normal and experimental oxygen uptake), O2 availability (blood O2 content.CBF), and O2 deficit (delta CMRO2.duration)] were assessed by stepwise and multiple linear regression. Levels of brain tissue carbohydrates (lactate, glucose, and glycogen) and energy metabolites [ATP, AMP, and creatine phosphate (CrP)] were significantly influenced by O2 deficit during hypoxia, as was final CMRO2. After 60 min of reoxygenation, levels of tissue lactate, glucose, ATP, and AMP were related statistically to the O2 deficit during hypoxia; however, CMRO2 changes were always associated more significantly with O2 availability during hypoxia. Creatine (Cr) and CrP levels in the brain following reoxygenation were correlated more to delta CMRO2 during hypoxia. Changes in some brain carbohydrate (lactate and glucose), energy metabolite (ATP and AMP) levels, and [H+]i induced by complete ischemia were also influenced by O2 deficit. After 60 min of postischemic reoxygenation, brain carbohydrate (lactate, glucose, and glycogen) and energy metabolite (ATP, AMP, CrP, and Cr) correlated with O2 deficit during ischemia. We conclude that "O2 deficit" is an excellent gauge of insult intensity which is related to observed changes in nearly two-thirds of the brain metabolites we studied during and following hypoxia and ischemia.     

Cellular levels, excretion, and synthesis rates of cyclic AMP in Escherichia coli grown in continuous culture.

Changes in dilution rate did not elicit large and systematic changes in cellular cyclic AMP levels in Escherichia coli grown in a chemostat under carbon or phosphate limitation. However, the technical difficulties of measuring low levels of cellular cyclic AMP in the presence of a large background of extracellular cyclic AMP precluded firm conclusions in this point. The net rate of cyclic AMP synthesis increased exponentially with increasing dilution rate through either the entire range of dilution rates examined (phosphate limitation) or a substantial part of the range (lactose and glucose limitations). Thus, it is probable that growth rate regulates the synthesis of adenylate cyclase. The maximum rate of net cyclic AMP synthesis was greater under lactose than under glucose limitation, which is consistent with the notion that the uptake of phosphotransferase sugars is more inhibitory to adenylate cyclase than the uptake of other carbon substrates. Phosphate-limited cultures exhibited the lowest rate of net cyclic AMP synthesis, which could be due to the role of phosphorylated metabolites in the regulation of adenylate cyclase activity. Under all growth conditions examined, greater than 99.9% of the cyclic AMP synthesized was found in the culture medium. The function of this excretion, which consumed up to 9% of the total energy available to the cell and which evidently resulted from elaborate regulatory mechanisms, remains entirely unknown.     

Cooperative binding is not required for activation of muscle phosphorylase.

Muscle and liver glycogen phosphorylase isozymes differ in their responsiveness to the activating ligand AMP. The muscle enzyme, which supplies glucose in response to strenuous activity, binds AMP cooperatively, and its enzymatic activity becomes greatly enhanced. The liver isozyme regulates the level of blood glucose, and AMP is not the primary activator. In muscle glycogen phosphorylase, the residue proline 48 links two secondary structural elements that bind AMP. This amino acid residue is replaced with a threonine in the liver isozyme; unlike the muscle enzyme, liver binds AMP noncooperatively, and the enzymatic activity is not greatly increased. We have substituted proline 48 in the muscle enzyme with threonine, alanine, and glycine and characterized the recombinant enzymes kinetically and structurally to determine if proline at this position is critical for cooperative AMP binding and activation. Importantly, all of the engineered enzymes were fully activated by phosphorylation, indicating that enzymatic activity was not compromised. Only the mutant enzyme with alanine at position 48 responds like the wild-type enzyme to the presence of AMP, indicating that proline is not absolutely required for full cooperative activation. The substitution of either threonine or glycine at this position, however, creates enzymes that no longer bind AMP cooperatively. The enzyme with threonine at position 48 further mimics the liver enzyme, in that the maximal enzymatic activity is also reduced. Significantly, the glycine substitution caused the enzyme to be fully activated by AMP, although binding was not cooperative. The hyperactivation of the glycine mutant by AMP suggests that the total free energy of activation has decreased.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regulation of glycogen metabolism in astrocytoma and neuroblastoma cells in culture.

The regulation of glycogen metabolism in C-6 astrocytoma and C-1300 neuroblastoma cells in culture has been investigated. Two modes of control of glycogen metabolism appear to be operative. The regulation of intracellular glycogen concentrations and the predominant forms of glycogen phosphorylase and glycogen synthase vary with (a) the available energy supply, and (b) altered intracellular concentration of cyclic adenosine 3':5'-monophosphate (cyclic AMP). Both cell lines respond to glucose in the medium; when glucose levels are high, glycogen is synthesized, glycogen phosphorylase a decreases, and glycogen synthase a increases. When glucose in the medium decreases to a critical level, the phosphorylase a increases and glycogen concentrations in the cells decrease in aprallel with the medium glucose. The critical glucose concentration is 2.5 mM for the astrocytoma cells and 4 mM for the neuroblastoma cells. Insulin promotes the conversion of phosphorylase to the b form and synthase to the a form in both cell lines. All of these changes occur without alteration in the intracellular cyclic AMP concentrations. When cyclic AMP concentrations are increased in either cell line, phosphorylase a is increased, synthase a is decreased, and glycogen concentrations decrease. Isobutyl methylxanthine is effective in promoting glycogenolysis in both cell lines. Norepinephrine is effective with the astrocytoma cells, and prostaglandin E1 is effective with the neuroblastoma cells.     

Regulation of Glycogenolysis in Transformed Astrocytes In Vitro

Cultured astrocytes, transformed by Herpesvirus, were used as a model system to study several aspects of the control of glycogenolysis. Adrenergic agonists such as norepinephrine and isoproterenol caused an immediate and dose-dependent increase in the intracellular levels of cyclic AMP. Concomitant with the initial phase of cyclic AMP increase, conversion of phosphorylase b to a and glycogenolysis were observed. The elevation of cyclic AMP, phosphorylase conversion, and glycogenolysis were simultaneously blocked by beta-adrenergic blockers, but not by alpha-adrenergic blocking agents. Repeated administration of norepinephrine caused an attenuated response in both cyclic AMP accumulation and glycogenolysis. Glycogen degradation is also partially regulated by glucose availability. In the presence of glucose, norepinephrine-induced glycogenolysis is blocked, despite elevations in cyclic AMP. The direct role of glucose is postulated, since glucose analogs mimic the effects of glucose.     

Regulation of lipogenesis in adipocytes. Independent effects of thyroid hormones, cyclic AMP and insulin on the uptake of deoxy-D-glucose.

Thyroidectomy is known to enhance fat cell phosphodiesterase activity; as a result, the response to lipolytic hormones is markedly reduced. Thyroidectomy also stimulates overall lipogenesis and the uptake of glucose: the present experiments investigated whether there was a correlation between cyclic AMP and glucose uptake. The parameter measured was the transport and phosphorylation (uptake) of deoxy-D-glucose in the presence of two modifiers of the cyclic AMP pool: phosphodiesterase inhibitors and the analogue, dibutyryl cyclic AMP. The inhibition by methylxanthines and dibutyryl cyclic AMP of deoxy-D-glucose uptake observed, was the same in fat cells from normal and thyroidectomized rats: the latter nonetheless still maintained their enhanced glucose uptake. It was therefore concluded that thyroid hormones and cyclic AMP control this step by different, separate pathways. Insulin, well known for its lipogenic effect, enhanced deoxy-D-glucose uptake in fat cells from both normal and thyroidectomized rats to the same extent (about 40%). An additive effect of thyroidectomy and insulin on glucose uptake was thus demonstrated. These results imply that glucose uptake in the adipocyte is controlled by at least three factors: thyroid hormones, cyclic AMP and insulin, each of which can act independently. Maximum glucose uptake is achieved in the presence of a combination of low concentrations of cyclic AMP, of insulin, and in the absence of thyroid hormones.     

Energy state of the liver during short-term and exhaustive exercise in C57BL/6J mice

A portal venous 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside infusion that results in hepatic 5-aminoimidazole-4-carboxamide-1-beta-D-ribosyl-5-monophosphate (ZMP) concentrations of approximately 4 micromol/g liver increases hepatic glycogenolysis and glucose output. ZMP is an AMP analog that mimics the regulatory actions of this nucleotide. The aim of this study was to measure hepatic AMP concentrations in response to increasing energy requirements to test the hypothesis that AMP achieves concentrations during exercise, consistent with a role in stimulation of hepatic glucose metabolism. Male C57BL/6J mice (27.4+/- 0.4 g) were subjected to 35 min of rest [sedentary (SED), n=8], underwent short-term (ST, 35 min) moderate (20 m/min, 5% grade) exercise (n=8), or underwent treadmill exercise under similar conditions but until exhaustion (EXH, n=8). Hepatic AMP concentrations were 0.82+/- 0.05, 1.17+/- 0.11, and 2.52+/- 0.16 micromol/g liver in SED, ST, and EXH mice, respectively (P< 0.05). Hepatic energy charge was 0.66+/- 0.01, 0.58+/- 0.02, and 0.33+/- 0.22 in SED, ST, and EXH mice, respectively (P< 0.05). Hepatic glycogen was 11.6+/- 1.0, 8.8+/- 2.2, and 0.0+/- 0.1 mg/g liver in SED, ST, and EXH mice, respectively (P< 0.05). Hepatic AMPK (Thr(172)) phosphorylation was 1.00+/- 0.14, 1.96+/- 0.16, and 7.44+/- 0.63 arbitrary units in SED, ST, and EXH mice, respectively (P< 0.05). Thus exercise increases hepatic AMP concentrations. These data suggest that the liver is highly sensitive to metabolic demands, as evidenced by dramatic changes in cellular energy indicators (AMP) and sensors thereof (AMP-activated protein kinase). In conclusion, AMP is sensitively regulated, consistent with it having an important role in hepatic metabolism.     

Dissociation of the effect of adrenalin on glucose uptake from that on adenosine cyclic 3′,5′-monophosphate levels and on lipolysis in rat-isolated fat cells

The effects of the adrenergic blocking agents phenoxybenzamine, phentolamine, indoramin and propranol on adrenalin-stimulated glucose uptake, lipolysis and cyclic AMP formation have been studied in rat-isolated fat cells. The β-adrenergic blocking agent propranolol was found to inhibit adrenaline-stimulated lipolysis and cyclic AMP formation at concentrations which did not inhibit adrenalin-stimulated glucose uptake. Conversely, the α-adrenergic blocking agent phenoxybenzamine inhibited adrenalin-stimulated glucose uptake at concentrations which did not inhibit lipolysis and cyclic AMP formation. The α-adrenergic blocking agents phentolamine and indoramin did not show differential effects on adrenalin-stimulated lipolysis and glucose uptake. Phenoxybenzamine had no effect on glucose uptake stimulated by insulin, adrenocorticotropic hormone and dibutyryl cyclic AMP. It is suggested that a substantial proportion of adrenalin-stimulated glucose uptake in rat-isolated fat cells is mediated by a mechanism not involving cyclic AMP. The adrenalin receptor was apparently α in type although the lack of effects of phentolamine and indoramin were not typical of those described on other α-systems.     

Similar and opposite effects of dibutyryl cyclic AMP and insulin on glucose metabolism in adipose tissue

The effects of N⁶-2′-O-dibutyryl cyclic AMP on glucose metabolism and lipolysis in fragments of rat epididymal adipose tissue were studied. Measurements were made of glucose uptake, conversion of glucose carbon to CO₂ and tissue fatty acids and glyceride-glycerol, lactate production, and glycerol release. Low concentrations of dibutyryl cyclic AMP (0.1–0.5 mM) increased all parameters of glucose metabolism and inhibited glycerol release in tissue from both normally fed and fasted rats. Higher concentrations of dibutyryl cyclic AMP (3–5 mM) diminished glucose utilization and greatly accelerated lipolysis. Insulin, 50 μunits/ml, accelerated glucose metabolism in the presence of either low or high concentrations of dibutyryl cyclic AMP though the effect of insulin was greatly reduced by 3 mM dibutyryl cyclic AMP. Tissue exposed to concentrations of dibutyryl cyclic AMP which inhibited glucose metabolism (5 mM), then rinsed and reincubated without dibutyryl cyclic AMP, displayed increased glucose utilization. The results of these experiments emphasize the need for caution in interpretation of the effects of dibutyryl cyclic AMP on adipose tissue metabolism and the need for further research to elucidate the role of cyclic AMP in the regulation of glucose metabolism.     

The effect of metabolites,papaverine, and probenecid on cyclic AMP efflux from isolated rat islets of Langerhans

The process of cyclic AMP efflux from rat islets of Langerhans has been studied. The dynamics of glucose-induced cyclic AMP efflux closely resembled the pattern of glucose-induced insulin release. Thus, both processes were dose-dependent for glucose having the same threshold concentrations (4–8 mmol/l glucose), with the time course of cyclic AMP efflux and insulin release from 0–60 min being very similar. Galactose did not affect insulin release, cyclic AMP efflux and intra-islet cyclic AMP accumulation. On the other hand, inosine, N-acetylglucosamine, α-ketoisocaproic acid, L-leucine and xylitol all promoted insulin release and cyclic AMP efflux. Except for L-leucine, all these substances enhanced the intracellular accumulation of cyclic AMP. The phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine, greatly augmented all these parameters in the presence of glucose whereas in the absence of glucose, insulin release was not enhanced, while both cyclic AMP efflux and cyclic AMP accumulation were elevated. The drug, probenecid, did not alter either insulin release or intra-islet cyclic AMP levels, while cyclic AMP efflux was markedly reduced (though not abolished). Papaverine inhibited both insulin release and cyclic AMP efflux, but was found to augment the intra-islet cyclic AMP levels. The efflux of cyclic AMP correlates more closely with insulin release than with the cyclic AMP accumulation in most instances. The efflux is independent of either insulin secretory granule extrusion or intracellular fluctuations of the nucleotide, though it is not yet known whether cyclic AMP efflux may have some regulatory significance in insulin release.     

Cyclic AMP transport across membrane vesicles of ultra-violet light irradiatedEscherichia coli

Transport of cyclic AMP acrossEscherichia coli membrane was studied using membrane vesicles. Uptake of cyclic AMP was measured using normally oriented vesicles, whereas uptake in everted vesicles was taken as a measure of the efflux of cyclic AMP. Ultra-violet irradiation of the cells led to an inhibition of both uptake and efflux of cyclic AMP across the membrane. The presence of cyclic AMP in the growth medium prior to ultra-violet irradiation caused an enhancement of the uptake and efflux. The uptake and efflux of cyclic AMP were less in vesicles from glucose grown cells as compared to the uptake and efflux by the vesicles prepared from glycerol grown cells. Similarly both uptake and efflux of cyclic AMP were more in vesicles prepared from cells grown on glycerol or glucose in the presence of cyclic AMP than in vesicles from cells grown in absence of cyclic AMP. It is suggested that the number of cyclic AMP carrier molecules were reduced in cells under catabolite repression by glucose as well as by ultra-violet irradiation     

Cyclic AMP, glucose and cortisol in plasma during surgery.

Cyclic AMP, glucose and cortisol in plasma were measured before, during and after major surgery (hysterectomy, six patients) and minor surgery (tympanoplasty, 10 patients). During major surgery cyclic AMP as well as glucose and cortisol showed a pronounced increase. During minor surgery cyclic AMP, glucose and cortisol levels were significantly lower than in the group undergoing major surgery. It is concluded that the increase of plasma cyclic AMP during operative procedures is related to the severity of the trauma.     

Effects of tri-n-butyltin chloride on energy metabolism, macromolecular synthesis, precursor uptake and cyclic AMP production in isolated rat thymocytes

The inhibitor of oxidative phosphorylation tri-n-butyltin chloride (TBTC) causes membrane damage and disintegration of isolated rat thymocytes at concentrations higher than 1 microM. From a concentration of 0.1 microM, TBTC disturbs energy metabolism as indicated by an increase in methylglucose uptake, glucose consumption and lactate production and by a decrease in cellular ATP levels. Over the same TBTC concentration range, the incorporation of DNA, RNA and protein precursors are markedly reduced. Moreover the production of cyclic AMP upon stimulation of the cells with prostaglandin E1 is effectively inhibited. These effects cannot be explained by an inhibition of nucleoside kinase activity, amino acid uptake or adenylate cyclase activity. The effects of TBTC on macromolecular synthesis and cyclic AMP production are possibly due to a disturbance of the cellular energy state.     

The role of adenosine 3′:5′-cyclic monophosphate in the regulation of insulin release by isolated rat islets of Langerhans

1. Concentrations of cyclic AMP (adenosine 3':5'-cyclic monophosphate) and rates of insulin release were measured in islets of Langerhans isolated from rat pancreas and incubated for various times in the presence of glucose, 3-isobutyl-1-methylxanthine, caffeine, theophylline, adrenaline and diazoxide. 2. Caffeine and theophylline produced small but significant increases in both cyclic AMP and release of insulin when they were incubated in the presence of 10mm-glucose. 3. 3-Isobutyl-1-methylxanthine produced a marked increase in the intracellular concentration of cyclic AMP in the presence of 5mm- and 10mm-glucose. However, insulin release was stimulated only in the presence of 10mm-glucose. 4. In response to rising concentrations of extracellular glucose (5-20mm) there was no detectable increase in the intracellular concentration of cyclic AMP even though there was a marked increase in the rate of insulin release. 5. In response to 10mm-glucose insulin release occurred in two phases and 3-isobutyl-1-methylxanthine potentiated the effect of glucose on both phases. The intracellular concentration of cyclic AMP remained constant with glucose and rose within 10min to its maximum value with 3-isobutyl-1-methylxanthine. 6. Adrenaline and diazoxide inhibited insulin release and lowered the intracellular concentration of cyclic AMP when islets were incubated with glucose or 3-isobutyl-1-methylxanthine. 7. It is suggested that glucose does not stimulate insulin release by increasing the concentration of cyclic AMP in islet cells. However, the concentration of cyclic AMP in islet cells may modulate the effect of glucose on the release process.     

Combined kinetic mechanism describing activation and inhibition of muscle glycogen phosphorylase b by adenosine 5'-monophosphate

The kinetic analysis of the glycogen chain growth reaction catalyzed by glycogen phosphorylase b from rabbit skeletal muscle has been carried out over a wide range of concentrations of AMP under the saturation of the enzyme by glycogen. The applicability of 23 different variants of the kinetic model involving the interaction of AMP and glucose 1-phosphate binding sites in the dimeric enzyme molecule is considered. A kinetic model has been proposed which assumes: (i) the independent binding of one molecule of glucose 1-phosphate in the catalytic site on the one hand, and AMP in both allosteric effector sites and both nucleoside inhibitor sites of the dimeric enzyme molecule bound by glycogen on the other hand; (ii) the binding of AMP in one of the allosteric effector sites results in an increase in the affinity of other allosteric effector site to AMP; (iii) the independent binding of AMP to the nucleoside inhibitor sites of the dimeric enzyme molecule; (iv) the exclusive binding of the second molecule of glucose 1-phosphate in the catalytic site of glycogen phosphorylase b containing two molecules of AMP occupying both allosteric effector sites; and (v) the catalytic act occurs exclusively in the complex of the enzyme with glycogen, two molecules of AMP occupying both allosteric effector sites, and two molecules of glucose 1-phosphate occupying both catalytic sites.     

Mycoplasma phosphoenolpyruvate-dependent sugar phosphotransferase system: glucose-negative mutant and regulation of intracellular cyclic AMP.

Glucose-negative mutants of Mycoplasma capricolum were selected for growth on fructose in the presence of the toxic glucose analog alpha-methyl-D-glucopyranoside. The mutants are defective in the phosphoenolpyruvate:sugar phosphotransferase system for glucose. One mutant, pts-4, was studied in detail. It lacks the glucose-specific, membrane-bound enzyme II, IIGlc, as well as the general, low-molecular-weight, phosphocarrier protein, HPr. In place of the latter, however, it has a fructose-specific protein, HPrFru. Consistent with these changes, the mutant lost the ability to grow on glucosamine and maltose but retained its ability to grow on sucrose. In the glucose-negative mutant, glucose did not regulate the intracellular concentration of cyclic AMP. The intracellular concentration of cyclic AMP in M. capricolum is regulated by the presence of metabolizable sugars. In the wild-type, both glucose and fructose reduced the intracellular concentration of cyclic AMP; however, in the glucose-negative mutant, glucose no longer regulated the intracellular level of cyclic AMP.