An enzyme histochemical study of isoproterenol-induced myocardial necroses in rats

Summary The effect of isoproterenol on myocardial metabolism in rats was studied using qualitative and quantitative histochemical techniques. The activity and location of 20 enzymes that play a role in the aerobic and anaerobic pathways of energy metabolism were qualitatively examined. The activity and location of some hydrolytic enzymes and the glycogen content were also qualitatively studied. For the quantitative study the activity of 10 enzymes was measured.The isoproterenol injections induced necrosis with inflammatory infiltrates. The muscle fibres in the necrotic regions were characterized by defective aerobic energy metabolism and increased glycolytic capacity. There was a depletion of the glycogen reserves in the necrotic fibres. These fibres showed a markedly increased activity of enzymes belonging to the oxidative branch of the pentose phosphate pathway. The implication of this increase for the metabolism of the myocardial cells is discussed. The activity of acid phosphatase in the pathological muscle fibres was strongly increased. The inflammatory cells in the necrotic areas were characterized by preponderantly anaerobic metabolism.Dedicated to Prof. H. G. Goslar in honour of his 70th birthday.     

Enzyme histochemical studies on the Purkinje fibres of the arrioventricular system of the bovine and porcine hearts

Synopsis In this communication the results of applying various histochemical semipermeable membrane techniques to the localization of several enzymes in bovine and procine heart are presented. The Purkinje fibres of the atrioventricular conducting system of the bovine heart differ from the myocardium proper in containing a greater activity of the glycolytic and gluconeogenetic enzymes—lactate dehydrogenase, glyceraldehyde-phosphate dehydrogenase, hexokinase, glucosephosphate isomerase and phosphoglucomutase, and less activity of the aerobic enzymes-NADH: nitroBT oxidoreductase and isocitrate dehydrogenase (NADP⁺). The metabolic reactions obtained with Purkinje fibres of the porcine heart are less pronounced. These histochemical findings are in accordance with the impression that Purkinje fibres, compared with the common myocardial fibres, have a higher rate of anaerobic metabolism and a lower rate of aerobic metabolism.The activity of the NADPH regenerating enzymes, glucose-6-phosphate dehydrogenase and phosphogluconate dehydrogenase (decarboxylating), and the activity of acid hydrolases such as non-specific esterase and acid phosphatase is higher in the Purkinje fibres of both the bovine and porcine heart.     

The increase in activity of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in skeletal muscles of rats after subcutaneous administration of N,N′-dimethyl-para-phenylenediamine

Summary After subcutaneous administration of N,N-dimethyl-para-phenylenediamine (DPPD) in rats, a myogenic myopathy was produced in the skeletal muscles. In this communication, the results of the application of various histochemical techniques for the localization of oxidoreductases, transferases, hydrolases and isomerases and biochemical techniques for the estimation of activities of oxidoreductases in the experimental skeletal muscles are presented. The most striking result was the activity of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase which increased dramatically during the early phase of the muscle disease. The increase in activity of the pentose phosphate shunt enzymes was the first pathological alteration and was present as early as 8 h after a single injection of DPPD. Histochemical techniques for demonstration of activity of both enzymes are therefore highly suited for the detection of minor diseases and the early onset of major diseases of the neuromuscular system. Some glycolytic enzymes as well as some enzymes of the aerobic part of the metabolism showed an early decrease or increase in activity indicating a metabolic imbalance in the muscle fibres. There were more fibres with an intermediate pattern of the energy yielding enzymes in the experimental muscle specimens then in specimens from the control groups. The activity of the catabolic hydrolytic enzymes was strongly increased in pathological muscles. The aerobic muscles were more vulnerable to DPPD than the anaerobic muscles.     

The value of enzyme histochemical techniques in the classification of fibre types of human skeletal muscle

Summary Classification of human skeletal muscle into type I and type II fibres is frequently based on their weak or strong staining with the myosin adenosine triphosphatase reaction. In order to evaluate the reliability of this screening technique a combined histochemical and biochemical study was performed on normal and diseased skeletal muscle of human subjects. In the present investigation activities of enzymes which play a role in the aerobic and anaerobic pathways and which can characterize fibre type, were examined in human muscle specimens with disease of the neuromuscular system.Special attention is given to the maximal activities of phosphofructokinase and fructose-1,6-diphosphatase, the rate limiting enzymes for the regulation of the glycolysis and gluconeogenesis respectively. Moreover the activities of enzymes of the pentose phosphate pathway are determined.A most important feature of the biochemical findings is that the constancy of activity ratios of the examined enzymes, as is found apparently normal human skeletal muscle, was frequently not present in diseased human skeletal muscle. From these results and from the histochemical results it can be concluded that for fibre classification in diseased human skeletal muscle the histochemical demonstration of myosin ATPase activity exclusively is not sufficient, but that it is necessary to apply other enzyme histochemical techniques too.Moreover it was found that in diseased human skeletal muscles the activity of the NADPH regenerating enzymes glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase was strongly increased. A third observation was the relative decrease of the activity of the examined aerobic enzymes in affected muscle fibres of neurogenic muscle diseases.     

Enzyme histochemical studies on the conducting system of the human heart

Summary In this communication, the results of applying various histochemical techniques for the localization of oxidoreductases, transferases, hydrolases and isomerases in the human heart are presented. The Purkinje fibres of the atrioventricular conducting system of the human heart differ from the myocardium proper in containing a slightly higher activity of most of the glycolytic and gluconeogenetic enzymes investigated. The relatively higher activity of 6-phosphofructokinase, the key enzyme in anaerobic carbohydrate metabolism, is especially noteworthy. On the other hand, the activities of some of the enzymes that play a part in the aerobic energy metabolism is slightly less than those in the myocardium fibres.As for the activity of the NADPH regenerating enzymes, the activity of 6-phosphogluconate dehydrogenase and malate dehydrogenase (oxaloacetate-decarboxylating) is somewhat higher, and the activity of glucose-6-phosphate dehydrogenase similar, in the Purkinje fibres compared to that in the myocardial fibres. The activity of myosin ATPase is similar for both types of fibre. Likewise, the fibres of the conducting system and of the myocardium show a similar activity of acid phosphatase, -glucuronidase, non-specific naphthylesterase and peroxidase. The neurogenic function of the conducting system of the human heart was demonstrated by the high activity of acetylcholinesterase in the Purkinje fibres and in the atrioventricular node. All these histochemical findings in Purkinje fibres are similar at widely differing levels of the conducting system.     

Enzyme histochemical studies on the Purkinje fibres of canine, bovine and porcine hearts

Synopsis Whereas in ungulates the Purkinje fibres of the atrioventricular conducting system are highly characteristic cells, those in the canine heart are poorly differentiated and accordingly they cannot always be readily identified in histological sections. Consequently in this paper the results of various histochemical tests on bovine and porcine hearts have been compared with the view of evaluating them as dependable methods for identifying Purkinje fibres that are microscopically poorly differentiated.It appeared that, histochemically, canine Purkinje fibres differ consistently in similar ways and as markedly from the common myocardial fibres as the morphologically typical conducting fibres in bovine and porcine hearts. The conducting fibres distinguish themselves from the myocardium proper in containing more glycogen and fewer lipids, in possessing higher activities of the enzymes -glucan phosphorylase,l-glycerol-3-phosphate:menadione oxidoreductase, myosin adenosine triphosphatase and monoamine oxidase, as well as in possessing lower activities of several dehydrogenases, cytochrome oxidase, peroxidase and mitochondrial adenosine triphosphatase. The relatively high activity of -glucan phosphorylase in particular is striking. As the activity of this enzyme persists during periods of up to 20 min after death, the staining method for this enzyme provides a valuable technique for identifying Purkinje fibres even if they are cytologically poorly differentiated.It is of interest in relation to electrophysiological data that the histochemical properties are similar in Purkinje fibres derived from widely differing levels of the conducting system. From the present histochemical findings it may be assumed that, as compared with the myocardium proper, the Purkinje fibres have a higher rate of anaerobic and a lower rate of aerobic metabolism. Furthermore, it is pointed out that histochemically the differences between Purkinje fibres and common myocardial cells on the one hand, and those between white (Type II) and red (Type I) striated muscle fibres on the other, are essentially similar.     

A comparative enzyme histochemical study of glucose metabolism in the conduction system of mammalian hearts.

A histochemical study of some enzymes of glucose metabolism was performed on the heart conduction system of rat, dog, rabbit, pig, calf and lamb. Histochemical activities revealed a higher rate of anaerobic metabolism and a lower rate of aerobic metabolism in the conducting cells in comparison with the working myocardial fibres. An increase of the histochemical activities from the atrioventricular node to the distal portions of bundle branches was noted. The importance of the high glycogen content and the high phosphorylase activity in the heart conduction system was discussed.     

The pentose phosphate pathway of glucose metabolism. Hormonal and dietary control of the oxidative and non-oxidative reactions and related enzymes of the cycle in adipose tissue

1. Measurements were made of the activities of the enzymes of the pentose phosphate pathway concerned in both the oxidative (glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase) and the non-oxidative (ribose 5-phosphate isomerase, ribulose 5-phosphate epimerase, transketolase and transaldolase) reactions of this pathway, together with hexokinase and phosphoglucose isomerase, in adipose tissue in a variety of nutritional and hormonal conditions. 2. Starvation for 2 days caused a significant decrease in the activities of all the enzymes of the pentose phosphate pathway, with the exception of glucose 6-phosphate dehydrogenase, when expressed as activity/2 fat-pads; only the activities of ribose 5-phosphate isomerase and ribulose 5-phosphate epimerase were significantly decreased on the basis of activity/mg. of protein. Re-feeding with a high-carbohydrate or high-fat diet for 3 days restored the activity of all the enzymes of the pentose phosphate pathway to the range of the control values, with the exception of transketolase, which showed a marked ;overshoot' in rats re-fed with carbohydrate. Starvation for 3 days caused a marked decrease in the activities of glucose 6-phosphate dehydrogenase and transketolase. 3. On the basis of activity/two fat-pads, alloxan-diabetes caused a marked decrease, to about half the control value, in the activities of all the enzymes concerned in the pentose phosphate pathway, transketolase showing the smallest decrease; hexokinase and phosphoglucose isomerase activities were also decreased. Treatment with insulin for 3 and 7 days raised the activities to normal or supranormal values, transketolase showing the most marked ;overshoot' effect. On the basis of activity/mg. of protein the activity of none of the enzymes was significantly decreased in alloxan-diabetes; transketolase and transaldolase activities were raised above the control values. With insulin treatment for 3 or 7 days the activities of all the enzymes were significantly increased, except that of ribulose 5-phosphate epimerase at the shorter time-interval. Glucagon treatment did not alter any of the enzyme activities expressed on either basis. 4. Thyroidectomy caused a decrease of 30-40% in the activities of enzymes of the pentose phosphate pathway, except for transketolase activity, which fell to 50% of the control value. Little change occurred in adipose-tissue weight or protein content. 5. Adrenalectomy caused a decrease of 40% in the activity of glucose 6-phosphate dehydrogenase and of 20-30% in the activities of the remaining enzymes of the pentose phosphate pathway; hexokinase activity was also decreased. Treatment with cortisone for 3 days did not significantly raise the activity from that found in adrenalectomized rats. Treatment of normal rats with high doses of cortisone had no significant effect on the activities of the enzymes of the pentose phosphate pathway in adipose tissue. 6. The changes in enzyme activities are discussed in relation to: (a) the concept of constant-proportion groups of enzymes; (b) the known changes in the flux of glucose through alternative metabolic pathways; (c) the pattern of change found in liver with similar hormonal and dietary conditions.     

In vivo measurements of control coefficients for hexokinase and glucose-6-phosphate dehydrogenase in Xenopus laevis oocytes

Hexokinase and glucose-6-phosphate dehydrogenase activities were increased in Xenopus laevis oocytes by microinjection of commercial pure enzymes. The effect of increased fractional activities on glycogen synthesis or on the production of 14CO(2) (the oxidative portion of the pentose phosphate pathway) was investigated by microinjection of [1-(14)C]glucose and measurements of the radioactivity in glycogen and CO(2). Control coefficients calculated from the data show that hexokinase plays an important role in the control of glycogen synthesis (control coefficient=0.7) but its influence on the control of the pentose phosphate pathway is almost nil (control coefficient=-0.01). Glucose-6-phosphate dehydrogenase injections did not affect the production of 14CO(2) by the pentose phosphate pathway, indicating that other factors control the operation of this pathway. In addition, an almost null control of this enzyme on glycogen synthesis flux was observed.     

Glycogen metabloism in the developing chick glycogen body: functional significance of the direct oxidative pathway.

Glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and glucose-6-phosphatase were quantitatively determined for the first time in glycogen body tissue from late embryonic and neonatal chicks. For comparative purposes, the activities of these enzymes were examined also in liver and skeletal muscle from pre- and post-hatched chicks. The present data show that both the embryonic and neonatal glycogen body lack glucose-6-phosphatase, but contain relatively high levels of glucose-6-phosphate dehydrogenase. The activity of each dehydrogenase in either embryonic or neonatal glycogen body tissue is two- to five-fold greater than that found in muscle or liver from pre- or post-hatched chicks. The relatively high activities observed for both dehydrogenases in the glycogen body, together with the absence of glucose-6-phosphatase activity in that tissue, suggest that the direct oxidative pathway (pentose phosphate cycle) of glucose metabolism is a functionally significant route for glycogen utilization in the glycogen body. It is hypothesized that the glycogen body is metabolically linked to lipid synthesis and myelin formation in the central nervous system of the avian embryo.     

The pentose phosphate pathway of glucose metabolism. Hormonal and dietary control of the oxidative and non-oxidative reactions of the cycle in liver

1. Measurements were made of the non-oxidative reactions of the pentose phosphate cycle in liver (transketolase, transaldolase, ribulose 5-phosphate epimerase and ribose 5-phosphate isomerase activities) in a variety of hormonal and nutritional conditions. In addition, glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities were measured for comparison with the oxidative reactions of the cycle; hexokinase, glucokinase and phosphoglucose isomerase activities were also included. Starvation for 2 days caused significant lowering of activity of all the enzymes of the pentose phosphate cycle based on activity in the whole liver. Re-feeding with a high-carbohydrate diet restored all the enzyme activities to the range of the control values with the exception of that of glucose 6-phosphate dehydrogenase, which showed the well-known ;overshoot' effect. Re-feeding with a high-fat diet also restored the activities of all the enzymes of the pentose phosphate cycle and of hexokinase; glucokinase activity alone remained unchanged. Expressed as units/g. of liver or units/mg. of protein hexokinase, glucose 6-phosphate dehydrogenase, transketolase and pentose phosphate isomerase activities were unchanged by starvation; both 6-phosphogluconate dehydrogenase and ribulose 5-phosphate epimerase activities decreased faster than the liver weight or protein content. 2. Alloxan-diabetes resulted in a decrease of approx. 30-40% in the activities of 6-phosphogluconate dehydrogenase, ribose 5-phosphate isomerase, ribulose 5-phosphate epimerase and transketolase; in contrast with this glucose 6-phosphate dehydrogenase, transaldolase and phosphoglucose isomerase activities were unchanged. Treatment of alloxan-diabetic rats with protamine-zinc-insulin for 3 days caused a very marked increase to above normal levels of activity in all the enzymes of the pentose phosphate pathway except ribulose 5-phosphate epimerase, which was restored to the control value. Hexokinase activity was also raised by this treatment. After 7 days treatment of alloxan-diabetic rats with protamine-zinc-insulin the enzyme activities returned towards the control values. 3. In adrenalectomized rats the two most important changes were the rise in hexokinase activity and the fall in transketolase activity; in addition, ribulose 5-phosphate epimerase activity was also decreased. These effects were reversed by cortisone treatment. In addition, in cortisone-treated adrenalectomized rats glucokinase activity was significantly lower than the control value. 4. In thyroidectomized rats both ribose 5-phosphate isomerase and transketolase activities were decreased; in contrast with this transaldolase activity did not change significantly. Hypophysectomy caused a 50% fall in transketolase activity that was partially reversed by treatment with thyroxine and almost fully reversed by treatment with growth hormone for 8 days. 5. The results are discussed in relation to the hormonal control of the non-oxidative reactions of the pentose phosphate cycle, the marked changes in transketolase activity being particularly outstanding.     

Employing a combinatorial expression approach to characterize xylose utilization in Saccharomyces cerevisiae

Fermentation of xylose, a major constituent of lignocellulose, will be important for expanding sustainable biofuel production. We sought to better understand the effects of intrinsic (genotypic) and extrinsic (growth conditions) variables on optimal gene expression of the Scheffersomyces stipitis xylose utilization pathway in Saccharomyces cerevisiae by using a set of five promoters to simultaneously regulate each gene. Three-gene (xylose reductase, xylitol dehydrogenase (XDH), and xylulokinase) and eight-gene (expanded with non-oxidative pentose phosphate pathway enzymes and pyruvate kinase) promoter libraries were enriched under aerobic and anaerobic conditions or with a mutant XDH with altered cofactor usage. Through characterization of enriched strains, we observed (1) differences in promoter enrichment for the three-gene library depending on whether the pentose phosphate pathway genes were included during the aerobic enrichment; (2) the importance of selection conditions, where some aerobically-enriched strains underperform in anaerobic conditions compared to anaerobically-enriched strains; (3) improved growth rather than improved fermentation product yields for optimized strains carrying the mutant XDH compared to the wild-type XDH.     

Presence of nonoxidative enzymes of the pentose phosphate shunt in Tetrahymena.

Tetrahymena pyriformis, strain HSM, do not have glucose-6-phosphate dehydrogenase or 6-phosphogluconate dehydrogenase, but contain transaldolase, transketolase, ribose 5-phosphate isomerase, ribulose-5-phosphate 3-epimerase, and ribokinase. The nonoxidative enzymes of the pentose phosphate shunt function in metabolism as indicated by the incorporation of label from [1-14C]ribose into CO2 and glycogen and by the increase in total glycogen content of cultures supplemented with ribose.     

The effect of aeration intensity on the biochemical composition of Baker's yeast: Activities of enzymes of the glycolytic and pentose phosphate pathways

A series of baker's yeast continuous cultivations were made using different intensities of aeration. The experimental conditions were such as to eliminate the effects caused by high glucose concentrations in the medium on the formation of enzymes. The variation in activity of several enzymes was investigated and distinct changes were noted. The activities of hexokinase and alcohol dehydrogenase characterize the actual rate of glycolysis in yeast, the same being true, in part, for pyruvate decarboxylase. The activity of phosphofructokinase is nearly insensitive to the oxygen level at normal tensions. The activity of the cell to the phosphofructokinase can be limited in anaerobic conditions by its scarcity. The insensitivity of glucose-6-phosphate dehydrogenase to the oxygen tension together with its low activity suggests that this enzyme plays primarily a biosynthetic role and that the function of the pentose phosphate pathway as an energy-producing route is negligible.     

Glycogen metabolism in the developing accessory lobes of Lachi in the nerve cord of the chick: metabolic correlations with the avian glycogen body

Glycogen synthase, glycogen phosphorylase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and glucose-6-phosphatase were determined for the first time in the necessary lobes of Lachi from late embryonic chicks. The activities of these enzymes were compared with those found in other glycogen-metabolizing tissues, specifically the glycogen body, liver, and skeletal muscle, obtained from the same embryos. The data show that, as in the glycogen body, the accessory lobes of Lachi lack glucose-6-phosphatase, but contain relatively high activity levels of glycogen synthase I, total and active glycogen phosphorylase, and the dehydrogenases of glucose-6-phosphate and 6-phosphogluconate. The percent of glycogen synthase I activity in the Lachi lobes is from two- to 20-fold greater than observed in the glycogen body, liver, or muscle, whereas the percent of glycogen phosphorylase a activity is comparable to that of the liver, but greater than that in the glycogen body or muscle. The activity of each dehydrogenase of the pentose phosphate cycle in the Lachi lobes is similar to that noted in the glycogen body, but is over two- or fivefold greater than that activity found in muscle or liver. Our data, together with other recent evidence, suggest that the role of glycogen in these functionally enigmatic tissues may be to support the precocious process of myelin synthesis in the developing bird, as well as possibly to provide alternate sources of energy for the avian central nervous system.     

Low temperature activation of post mortem glycogenolysis in bovine skeletal muscle fibres.

Synopsis Trimmed strips of stermomandibularis muscles taken from freshlyslaughtered cattle were placed in an isotonic myograph and cooled to 1°C. Spontaneous activity due to neuromuscular irritability was minimized by keeping muscle surfaces moist and anaerobic and was monitored by electromyography. Muscle strips were removed and frozen for histochemical analysis after they had completed their initial phase of cold-induced shortening (several hours). Control strips maintained for an equal time at 24°C rarely depleted the stainable glycogen in any of their muscle fibres so as to become PAS-negative. In chilled muscle strips, however, glycogenolysis was activated in some muscle fibres and they became PAS-negative. In serial sections, most of the PAS-negative fibres exhibited strong ATPase and weak succinate dehydrogenase activity. Fibres with weak ATPase and strong succinate dehydrogenase activity rarely became PAS-negative. These results are in agreement with biochemical reports of a cold-induced (<5°C) activation of glycolysis in skeletal musclepost mortem. Investigations on untrimmed lengths of excised sternoman dibularis muscle indicated that longitudinal muscle damage caused in cutting muscle strips for the myograph and/or their more rapid rate of initial cooling had facilitated the depletion of stainable glycogen.     

Glycogen-enzymes containing bodies in type 2 fibres of tenotomized muscles in the rat

Inclusion bodies containing glycogen-enzymes were found in 30 to 60% of type 2 fibres of tenotomized calf muscles (m. gastrocnemius, m. soleus, m. plantaris) in rats, using histochemical reactions. The bodies appeared within 1 week after the tenotomy and were localized both in the central and the subsarcolemmal regions and rarely extruded into the extracellular space. These aggregates are 3 to 15 microns in length and 2 to 11 microns in diameter. In addition to glycogen, these bodies also contained various enzymes of the glycogen metabolism such as phosphorylase, a branching enzyme, and glucose-6-phosphatase, but showed no NADH-reductase, lactate dehydrogenase, or myofibrillar ATP-ase activity. The results indicate that glycogen-enzymes containing bodies are a degenerative phenomenon, which occurs only in type 2 fibres of the tenotomized muscles.     

Correlative histochemical studies on preneoplastic and neoplastic lesions in the kidney of rats treated with nitrosamines

Renal tubular lesions induced in male rats by two different carcinogens, N-nitrosomorpholine (NNM) and N-ethyl-N-hydroxyethylnitrosamine (EHEN), using a limited exposure "stop" protocol were investigated histochemically to demonstrate phenotypic cellular changes. The parameters measured included basophilia, glycogen content and the activity of the enzymes glucose-6-phosphatase (G6PASE), glycogen synthetase (SYN), glycogen phosphorylase (PHO), glucose-6-phosphate dehydrogenase (G6PDH), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), succinate dehydrogenase (SDH), alkaline phosphatase (ALP), acid phosphatase (ACP) and gamma-glutamyl transpeptidase (gamma-GT). The lesions observed were predominantly of either basophilic or oncocytic types. In each case, tubular lesions (altered tubules) appeared to give rise to epithelial tumors (epitheliomas) with the same cellular phenotype. Basophilic tubules and epitheliomas proved to be strongly positive for GAPDH and G6PDH while demonstrating a reduction or loss of G6PASE, ALP, ACP, gamma-GT, and SDH compared with controls and the surrounding proximal or distal tubules. In addition, large basophilic epitheliomas demonstrated an increase in both SYN and PHO activities. In contrast, most oncocytic tubules and oncocytomas characterized by abundant densely granular cytoplasm showed a reduction in the activity of G6PDH, but were intensely positive for SDH. However, a few oncocytic lesions demonstrated a decrease in both SDH and G6PDH activity. Rarely, decreased SDH and elevated G6PDH activities were observed in altered tubules resembling oncocytic tubules. It remains to be clarified whether these tubules represent a variation of the oncocytic lesions or, perhaps, another type of tubular lesion. The results indicate that basophilic and oncocytic epithelial tumors differ in their cytochemical pattern and histogenesis. In line with earlier suggestions, the basophilic tumors apparently originate from the proximal renal tubules, while the oncocytomas develop from the distal parts of the nephron. The basophilic tumors are characterized by an increased pentose phosphate pathway and glycolysis, with a corresponding reduction in mitochondrial respiration. However, the majority of the oncocytomas show an increased activity of the mitochondrial enzyme SDH, and a marked decrease in the activity of the key enzyme of the pentose phosphate pathway.     

Glucose Metabolism in Neisseria gonorrhoeae

The metabolism of glucose was examined in several clinical isolates of Neisseria gonorrhoeae. Radiorespirometric studies revealed that growing cells metabolized glucose by a combination on the Entner-Doudoroff and pentose phosphate pathways. A portion of the glyceraldehyde-3-phosphate formed via the Entner-Doudoroff pathway was recycled by conversion to glucose-6-phosphate. Subsequent catabolism of this glucose-6-phosphate by either the Entner-Doudoroff or pentose phosphate pathways yielded CO(2) from the original C6 of glucose. Enzyme analyses confirmed the presence of all enzymes of the Entner-Doudoroff, pentose phosphate, and Embden-Meyerhof-Parnas pathways. There was always a high specific activity of glucose-6-phosphate dehydrogenase (EC 1.1.1.49) relative to that of 6-phosphogluconate dehydrogenase (EC 1.1.1.44). The glucose-6-phosphate dehydrogenase utilized either nicotinamide adenine dinucleotide phosphate or nicotinamide adenine dinucleotide as electron acceptor. Acetate was the only detectable nongaseous end product of glucose metabolism. Following the disappearance of glucose, acetate was metabolized by the tricarboxylic acid cycle as evidenced by the preferential oxidation of [1-(14)C]acetate over that of [2-(14)C]acetate. When an aerobically grown log-phase culture was subjected to anaerobic conditions, lactate and acetate were formed from glucose. Radiorespirometric studies showed that under these conditions, glucose was dissimilated entirely by the Entner-Doudoroff pathway. Further studies determined that this anaerobic dissimilation of glucose was not growth dependent.