The noninvolvement of MDH as NAD-oxidoreductase shuttle in rat liver peroxisomes

Subcellular localization of malate dehydrogenase and glycerol-3-phosphate dehydrogenase in rat liver was studied by sucrose density gradient centrifugation. The specific adsorption of cytosolic malate dehydrogenase to the peroxisomes was observed. This phenomenon was eliminated by washing peroxisome-rich fraction with 100 mM potassium chloride. It is suggested that the malate shuttle between the cytosol and the mitochondria is more dominant than the glycerophosphate shuttle with respect to the transfer of reducing equivalents, while NADH produced by fatty acid oxidation in peroxisomes can not be transferred into the cytosol via the malate shuttle in the rat liver.

Microsomal and lysosomal enzymes of triacylglycerol metabolism in rat placenta

The placenta plays a major role in transporting lipid to the developing foetus. Since previous studies have suggested that placental lipid transport involves intermediate esterification steps, we investigated selected microsomal and lysosomal enzymes of triacylglycerol metabolism in rat placenta. Between gestational days 10 and 14, microsomal phosphatidic acid phosphatase specific activity was 6-fold greater than the activity in adult rat liver. Phosphatidic acid phosphatase activity decreased 50% on day 15. Studies employing several different phosphorylated substrates indicated a high degree of substrate specificity. Lysosomal triacylglycerol lipase and cholesterol esterase activities decreased about 50% between days 15 and 18, then rose late in gestation. No changes were observed in the specific activities of fatty acid: CoA ligase, glycerolphosphate acyltransferase, lysophosphatidate acyltransferase, diacylglycerol acyltransferase or diacylglycerol cholinephosphotransferase during the final 12 days of gestation. Kinetic observations (competitive inhibition by alternative substrates, pH-dependence and thermal inactivation) were consistent with the hypothesis that glycerol phosphate and dihydroxyacetone phosphate can be acylated by a single microsomal enzyme in placenta. Except for fatty acid: CoA ligase, the activities of microsomal and lysosomal enzymes of triacylglycerol metabolism were comparable with those in adult rat liver. These observations are consistent with physiological studies suggesting that triacylglycerol synthetic and degradative pathways are very active in rat placenta.

Characterization of a subset of oligodendrocytes separated on the basis of selective adherence properties

A subset of oligodendrocytes (B3,f) was isolated by taking advantage of selective cell-substratum interaction. B3,f cells were characterized morphologically, biochemically, and immunocytochemically. Oligodendrocytes were isolated from 4-to-6-month-old lamb brains by a modified version of our published procedure [Szuchet et al, J Neurosci Methods 3:7-19, 1980]. Freshly isolated cells from band III were plated on plastic culture plates at a concentration of 2 X 10(6) cells/ml. Approximately 40% of the cells attached to the plate under these conditions. The remaining cells formed small floating clusters. We refer to the latter as B3,f oligodendrocytes. After 4 to 5 days, the supernatant containing B3,f cells was removed and centrifuged, and the pellet was resuspended in culture medium and replated on polylysine-coated petri dishes. B3,f oligodendrocytes attached to this surface and extended an intricate network of processes. The purity of the cultures, judged by the number of cells staining with a monoclonal antibody against galactocerebroside was 98-99%. This high degree of cell homogeneity was maintained throughout the life of the cultures. B3,f cells appeared to be highly differentiated and remained so in vitro. This is surmised by the expression of oligodendrocytic characteristic functions such as high levels of CNPase activity typically, 5 microM/min/mgP; high incorporation of H2 35SO4 into sulfatides, an overall lipid metabolism that mimics events associated with myelinogenesis [Szuchet et al, PNAS 80:7019-7023, 1983]; the presence, detected immunocytochemically, of myelin-associated glycoprotein and myelin basic proteins. It is concluded that this culture system offers an opportunity for studying the biology of interfascicular oligodendrocytes and their interaction with neurons and/or astrocytes. It also should open up a way of examining the relevance of oligodendrocyte polymorphism.

Development of enzymes of energy metabolism in rat heart

The behavior of several enzymes was studied during rat heart development (4 days before birth to adult stage). Hexokinase has its highest activity during the fetal period; it decreases at birth and remains with low activity in the adult. The alpha-glycerophosphate dehydrogenase and alpha-glycerophosphate oxidase profiles are similar up to the 15th day of development. From there onwards, both profiles diverge, the cytoplasmic activity increasing 3-fold, while the mitochondrial activity remains unchanged. The developmental profiles of the malate dehydrogenases are almost parallel. The development of citrate synthase and succinate dehydrogenase results in a 2- to 4-fold increase in their activities. However, ATPase increases dramatically (20-fold) over the same period. With respect to the enzymes of the adenine nucleotide metabolism, adenylate kinase is fully expressed throughout all ages examined, showing no variation during development. AMP deaminase and creatine kinase increase during development, the cytoplasmic creatine kinase reaching a high level at birth whereas the increases of the mitochondrial enzymes take place gradually during development.

The effect of prolonged fasting on total lipid synthesis and enzyme activities in the liver of the European eel (Anguilla anguilla)

The extent of fatty acid synthesis from [1-14C]acetate in liver slices was reduced 6-fold when eels were fasted for 1-7 weeks and 20-fold when fasted for 39 weeks; thereafter hepatic lipogenesis seemed to remain constant for up to 95 weeks of fasting. After a 1-3 week fast some hepatic enzyme activities were reduced (acetyl-CoA carboxylase decreased 2-fold and fatty acid synthetase declined 5-fold), while others remained unchanged (glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, alpha-glycerol phosphate dehydrogenase as well as malic enzyme and ATP-citrate lyase). The optimum temperature for measuring both total lipid synthesis and lipogenic enzyme activity in eel liver was found to be 30 degrees C.

The molecular basis for adrenergic desensitization in hamster brown adipose tissue: uncoupling of adenylate cyclase activation

A crude membrane fraction was prepared from hamster brown adipose tissue. Extensive washing of the crude membranes was crucial for the appearance of specific beta-adrenergic receptor binding as assessed by (-)-[3H]dihydroalprenolol. Adrenergic agents competed for the specific binding sites with beta 1-specificity. Binding characteristics were very similar to those earlier found in intact cells, supporting our previous finding that a single (non-tumour) mammalian cell may contain as many as 60,000 beta-adrenergic receptors. Desensitization in situ (i.e. chronic norepinephrine stimulation due to cold acclimation) only marginally affected the number of beta 1-receptors and their affinity (Ki) for norepinephrine. Total (fluoride-stimulated) adenylate cyclase increased somewhat, but the Kact for norepinephrine slightly decreased. Thus the ratio Ki/Kact was rather unaffected by cold acclimation. However, the fraction of adenylate cyclase which could be stimulated by norepinephrine decreased drastically. GTP introduced a low-affinity form (for agonist) of the receptor. The form observed in isolated cells must primarily be the high-affinity form. The basis for desensitization must reside in a diminished ability to transfer the signal from the receptor to the cyclase. This change may be molecularly located in the N-protein or in its interaction with the receptor.

Subcellular origin of the surface fluorescence of reduced nicotinamide nucleotides in the isolated perfused rat heart

Surface fluorometric measurements and indicator metabolite determinations in the isolated perfused rat heart showed that the NADH + NADPH fluorescence of the intact tissue originates largely from the mitochondria. The redox potential of the lactate dehydrogenase system calculated from the endogenous lactate/pyruvate ratios was closely similar to that of the glycerol-3-phosphate dehydrogenase system calculated from the concentrations of glycerol-3-phosphate and dihydroxyacetone phosphate in the tissue. Thus, in contrast to the liver, the cytosolic redox state of the NADH/NAD+ system in isolated perfused heart oxidizing external glucose or fatty acid is not amenable to optical monitoring, but can be assessed from the state of the lactate dehydrogenase or glycerol-3-phosphate dehydrogenase systems.

Glial cells dissociated from newborn and aged mouse brain

Changes occurring with days in culture and cell passage in cultured glial cells derived from newborn vs aged (18-mo) mouse cerebral hemispheres were compared. The activities of the enzymes glutamine synthetase (GS), an astrocyte marker, and 2',3'-cyclic nucleotide 3'- phosphohydrolase (CNP), an oligodendrocyte marker, were determined. In addition, glial fibrillary acidic protein (GFA) and glycerol phosphate dehydrogenase (GPDH) immunoreactivity was used to morphologically identify astrocytes and oligodendrocytes, respectively. In cultures derived from newborn mouse cerebral hemispheres, both GS and CNP activity and GFA-positive and GPDH-rhodamine-positive cells were present with cell passage. In general, GS activity did not change in early cell passage in cultures from either newborn or aged mouse; in passage 5, GS was high in both sources of cell populations. CNP activity increased with cell passage in cultures derived from newborn mouse; in cultures derived from aged mouse CNP was low in the primary cultures, increased with cell passages 2 and 3, and declined with passages 4 and 5. The survival of astrocytes as shown by GS and the decline in oligodendrocytes as shown by CNP was also supported by an increase in the proportions of GFA and GPDH immunoreactive cells. We interpret the increase in GS activity to parallel the astrogliosis observed in vivo in the aging brain. Moreover, the decline in oligodendrocytes in culture may represent a shift of balance between glial cell types that appears to be influenced by the age of brain tissue and time in culture.

Characterization of succinate dehydrogenase and alpha-glycerophosphate dehydrogenase in pancreatic islets

Succinate dehydrogenase activities in homogenates of rat and ob/ob mouse pancreatic islets were only 13% of the activities in homogenates of liver and were also several times lower than in homogenates of pancreatic acinar tissue. This indicates that the content of mitochondria in pancreatic islet cells is very low. The very low activity of succinate dehydrogenase is in agreement with the low mitochondrial volume in the cytoplasmic ground substance of pancreatic islet cells as observed in morphometric studies. This may represent the poor equipment of pancreatic islet cells with electron transport chains and thus provide a regulatory role for the generation of reducing equivalents and chemical energy for the regulation of insulin secretion. The activities of succinate dehydrogenase in tissue homogenates of pancreatic islets, pancreatic acinar tissue, and liver were significantly inhibited by malonate and diazoxide but not by glucose, mannoheptulose, streptozotocin, or verapamil. Tolbutamide inhibited only pancreatic islet succinate dehydrogenase significantly, providing evidence for a different behavior of pancreatic islet cell mitochondria. Therefore diazoxide and tolbutamide may affect pancreatic islet function through their effects on succinate dehydrogenase activity. The activities of alpha-glycerophosphate dehydrogenase in homogenates of pancreatic islets and liver from rats and ob/ob mice were in the same range, while activities in homogenates of pancreatic acinar tissue were lower. None of the test agents affected alpha-glycerophosphate dehydrogenase activity. Thus the results provide no support for the recent contention that alpha-glycerophosphate dehydrogenase activity may be critical for the regulation of insulin secretion.

Evidence of an age-related decline in mitochondrial glycerophosphate dehydrogenase activity of isolated rat islets

The activities of three enzymes--two mitochondrial and one microsomal--were measured in isolated islets of Langerhans from 2-month-old and 12-month-old rats. Mitochondrial glycerophosphate dehydrogenase activity (expressed as nanomoles of iodonitrotetrazolium reduced per minute per milligram of protein), decreased (P less than 0.01) from a mean (+/- SEM) of 73.2 +/- 11.2 (2-month-old) to 34.7 +/- 5.9 (12-month-old). In contrast, activities of neither mitochondrial monoamine oxidase nor microsomal NADH cytochrome-c reductase changed with age. These results demonstrate that the activity of the glycerophosphate shuttle decreases as rats grow older, and it raises the possibility that the consequent difficulty in regenerating cytosolic NAD+ may play a role in the insulin secretory defect associated with aging.

Unique modification of human heart glycerol 3-phosphate dehydrogenase by blue agarose

The major form of glycerol phosphate dehydrogenase in human heart (GPDH-1) is a minor form (less than 15%) in brain and other tissues and is extremely labile. After GPDH-1 was eluted from an agarose column to which Cibacron blue F3GA had been covalently linked, (a) it was no longer labile (t 1/2 at 40 degrees C changed from 1.6 min to greater than 180 min); (b) it could now be stained for activity on native gels following electro-phoresis; and (c) it now migrated with the bromphenol blue dye front. The results suggest that this stabilized form of GPDH-1 is due to the covalent binding of charged ligands from the column and that this technique may be useful for studying the molecular structure and/or the active site of GPHD-1 and possibly of other enzymes which bind to blue agarose.

Distribution and metabolism of L- and D-triiodothyronine (T3) in the rat: preferential accumulation of L-T3 by hepatic and cardiac nuclei as a probable explanation of the differential biological potency of T3 enantiomers

Previous studies have reported markedly lower biological potency of D-T3 than would be predicted from its relative affinity for the specific nuclear L-T3 receptor as measured in vitro. Studies were undertaken to define the basis of this discrepancy. In vitro studies of the relative binding affinities of [125I]L-T3 and [125I]D-T3 using either whole nuclei or partially purified solubilized receptor confirmed several previous reports which had indicated only small relative differences. The mean L/D binding ratio of all in vitro studies was 1.43. In contrast, we determined from measurement of final alpha-glycerophosphate dehydrogenase activity that the potency ratio (L/D) after seven daily injections of graded doses of L- and D-T3 was 6.7 for liver, with 95% confidence limits of 4.1 to 10.8, and 15.9 for heart, with 95% confidence limits of 5.1 to 50.2. Difference in biological potency could not be attributed to differences in the metabolism of L- and D-T3. Thus, tracer [125I]L- and [125I]D-T3 studies showed that the mean residence time, t, of L-T3 was not different from that of D-T3 [10.6 +/- (SE) 3.1 h vs. 11.4 +/- 3.8 h]. The MCR for L-T3 was 19.1 +/- 4.4 ml/h . 100 g BW and for D-T3, 26.1 +/- 5.6 ml/h . 100 g BW. The volume of distribution of L-T3 (181 ml/100 g BW) was 68% that of D-T3 (263 ml/100 g BW), in part owing to the 27% greater plasma binding (bp) of L-T3. Moreover, the calculated free hormone clearance (MCR X bp) of D-T3 was only 8% greater than for L-T3. Throughout the 24 h after injection of the [125I]L- or D-T3, concentrations of the D-enantiomer in liver were almost twice those of [125I]L-T3, whereas in heart [125I]D-T3 concentrations were half or less those of [125I]L-T3. Nevertheless, in both liver and heart, the integrated nuclear occupancy of L-T3 was 5 to 6 times that of D-T3, approaching the ratio in biological potency observed in the tissues. Thus, selective nuclear binding of L-T3 vs. D-T3 in vivo appears to be a major determinant in the relative biological effects of these enantiomers.

Naturally occurring genetic variation affecting the expression of sn-glycerol-3-phosphate dehydrogenase in Drosophila melanogaster

Genetic variation among second and third chromosomes from natural populations of Drosophila melanogaster affects the activity level of sn-glycerol-3-phosphate dehydrogenase (EC 1.1.1.8; GPDH) at both the larval and the adult stages. The genetic effects, represented by differences among chromosome substitution lines with coisogenic backgrounds, are very repeatable over time and are generally substantially larger than environmental and measurement error effects. Neither the GPDH allozyme, the geographic origin, nor the karyotype of the chromosome contributes significantly to GPDH activity variation. The strong relationship between GPDH activity level and GPDH-specific CRM level, as well as our failure to find any thermostability variation among the lines, indicates that most, if not all, of the activity variation is due to variation in the steady-state quantity of enzyme rather than in its catalytic properties. The lack of a strong relationship between adult and larval activity levels suggests the importance of stage- or isozyme-specific effects.

Increased mitochondrial glycerol phosphate dehydrogenase activity in insulinomas of two hypoglycemic infants

The activities of flavin-linked, mitochondrial glycerol phosphate dehydrogenase in islet cell adenomas from two infants were 8 and 16 times higher than those in their uninvolved pancreases. The enzyme in the insulinomas, but not that in the nearby pancreases, was inhibited by diazoxide, which is a known inhibitor of insulin secretion in vitro and in vivo. These results provide preliminary evidence that the enzyme may be used as an adjunct to histology for identifying human insulin-secreting tissues. Its sensitivity to diazoxide adds specificity to the test. Taken together with previous work with animal pancreatic islets, the results of the present study suggest that the glycerol phosphate shuttle plays an important role in stimulus-secretion coupling in the pancreatic beta-cell.

Absence of alpha-glycerophosphate dehydrogenase in axenically grown Entamoeba histolytica

We conclude that there is no evidence for the presence of alpha-glycerophosphate dehydrogenase among the cytoplasmic enzymes of Entamoeba histolytica, and that a contrary finding was probably caused by the action of a different amebal enzyme on unrecognized contamination in the lithium salt of the substrate used in that investigation.

Growth and adipose differentiation of sheep preadipocyte fibroblasts in serum-free medium

Fibroblasts from ovine skin, and from the perirenal and subcutaneous adipose tissues of sheep were grown at clonal densities in medium MCDB 202 supplemented with 1 microgram/ml bovine insulin, 1 microM dexamethasone, 100 ng/ml fibroblast growth factor and 20 micrograms/ml of the lipid preparation described by Bettger, W. J., Boyce, S. T., Walthall, B. J. and Ham, R. G. [(1981) Proc. Natl Acad. Sci, USA, 78, 5588-5592]. When maintained as a confluent monolayer in this medium, the fibroblasts from the adipose tissues spontaneously underwent an adipose differentiation. This was accelerated by substituting medium F12 for medium MCDB 202, and by raising the CO2 tension from 2% to 7.5% in air over the cultures. The differentiation was inhibited by deleting FGF from the growth medium, or by coating the culture surface with fibronectin or poly-D-lysine. Differentiation also failed to occur when the defined supplements were replaced with fetal bovine serum. The synthesis of triacylglycerol by the cells, as seen by the increased specific activity of [14C]acetate incorporated into this lipid class, was accompanied by an increase in the specific activity of glycerol-3-phosphate dehydrogenase.

Modulation of lipid-synthesizing enzymes by insulin in differentiated ob17 adipose-like cells

ob17 cells convert into adipose-like cells when maintained in the presence of physiological concentrations of insulin and tri-iodothyronine. After this conversion, insulin removal from differentiated ob17 cells gives within 24-48 h a large decrease in fatty acid synthetase, glycerol 3-phosphate dehydrogenase and acid:CoA ligase activities, as well as in the rate of fatty acid synthesis determined by [14C]acetate incorporation into lipids. All parameters are restored by insulin addition to initial values within 24-48 h. Dose-response curves of insulin on the restoration of glycerol 3-phosphate dehydrogenase activity and of fatty acid synthesis give half-maximally effective concentrations close to 1 nM, in agreement with the affinity for insulin of the insulin receptors previously characterized in these cells. Immunotitration experiments indicate that the changes in the specific activity of fatty acid synthetase are due to parallel changes in the cellular enzyme content. Therefore the ob17 cell line should be a useful model to study the long-term effects of insulin on the modulation of lipid synthesis in adipose cells.

Postnatal growth and differentiation of muscle fibres in the mouse. I. A histochemical and morphometrical investigation of normal muscle

A histochemical classification of muscle fibres based on three enzymes (ATPase, pre-inc. pH 4:35; succinic dehydrogenase and alpha-glycerol-phosphate-dehydrogenase) was used to describe postnatal growth and differentiation of muscle fibres. The m. soleus, m. plantaris and m. gastrocnemius were examined in normal mice from birth to the young adult stage. At birth, differentiation of the gastrocnemius muscle was in a more advanced stage than that of the plantaris and the soleus muscles, while the last of these was the least developed. During growth, as well as in the (young) adult, there was a distinct relation between fibre type and size, which, however, differed per muscle (region). The development of muscle fibres was a gradual process, rather than a succession of distinct stages, although a change in fibre type was often accompanied by a change in size. Differentiation of fibres already occurred perinatally, and the "adult fast' fibre types appeared during the second week postnatally, varying with the muscle region. During development, a percentage of fibres remained as a population that was histochemically and morphometrically intermediate between the fast-oxidative-glycolytic and fast-glycolytic adult fibres. A model is presented in which the most probable pathways of development are depicted.

Regulation of sn-glycerol-3-phosphate dehydrogenase in Drosophila melanogaster larvae by dietary ethanol and sucrose

Dietary sucrose and ethanol are potent modulators of sn-glycerol-3-phosphate dehydrogenase (GPDH) in the third instar larvae of Drosophila melanogaster. When added to modified Sang's medium C, 428 mM ethanol and 146 mM sucrose each increased the GPDH tissue activity more than 90% and GPDH cross-reacting material (CRM) more than 50% over the levels found in larvae fed the 14.6 mM sucrose control diet. When fed together, ethanol and sucrose exerted synergetic effects on GPDH activity and CRM. The activity of glycerol-3-phosphate oxidase was also stimulated by dietary ethanol and sucrose, indicating that the glycerol-3-phosphate cycle was operating in the larvae. Dietary ethanol caused similar shifts in the NADH:NAD+ ratio in wild-type and Gpdh null larvae, suggesting that the maintenance of the cofactor equilibrium is not the primary function of GPDH in larvae. Increases in triacylglycerol content associated with the administration of ethanol and sucrose to larvae suggested that the formation of glycerol-3-phosphate for use in lipid synthesis is an important function of GPDH in larvae. Because ethanol is a constituent of the natural diet of D. melanogaster, nutritional modulation of GPDH is postulated to be an important aspect of the adaptation of the species to its environment.

A histochemical and enzymatic study of the muscle fiber types in the water monitor, Varanus salvator

Histochemical analysis of five muscles from the water monitor, Varanus salvator, identified three major classes of fibers based on histochemical activities of the enzymes myosin ATPase (mATPase), succinic dehydrogenase (SDH), and alpha-glycerophosphate dehydrogenase (alpha GPDH). Fast-twitch, glycolytic (FG) fibers were the most abundant fiber type and exhibited the following reaction product intensities: mATPase, dark; SDH, light; alpha GPDH, moderate to dark. Fast-twitch, oxidative, glycolytic (FOG) fibers were characteristically mATPase, dark; SDH, light; alpha GPDH, moderate to dark. The third class of fibers had the following histochemical characteristics: mATPase, light; SDH, moderate to dark; alpha GPDH, light. These fibers were considered to be either slow twitch, or tonic, and oxidative (S/O). Pyruvate kinase (PK), alpha GPDH, and citrate synthase (CS) activities were measured in homogenates of the same muscles studied histochemically. There was a positive relationship between both PK and alpha GPDH activities and the percentage of glycolytic fiber types within a muscle. Likewise, CS activities were greater in muscles high in FOG and S/O content. Based on CS activities, Varanus S/O fibers were eight-fold more oxidative than FG fibers within the same muscle. PK/CS ratios suggested that FG fibers possess high anaerobic capacity, similar to the iguanid lizard Dipsosaurus. The fiber type composition of the gastrocnemius muscle, relative to that of other lizard species, suggests that varanid lizards may possess a greater proportion of FOG and S/O fibers than other lizards.

sn-Glycerol-3-phosphate transport in Salmonella typhimurium

Salmonella typhimurium contains a transport system for sn-glycerol-3-phosphate that is inducible by growth on glycerol and sn-glycerol-3-phosphate. In fully induced cells, the system exhibited an apparent Km of 50 microM and a Vmax of 2.2 nmol/min . 10(8) cells. The corresponding system in Escherichia coli exhibits, under comparable conditions, a Km of 14 microM and a Vmax of 2.2 nmol/min . 10(8) cells. Transport-defective mutants were isolated by selecting for resistance against the antibiotic fosfomycin. They mapped in glpT at 47 min in the S. typhimurium linkage map, 37% cotransducible with gyrA. In addition to the glpT-dependent system, S. typhimurium LT2 contains, like E. coli, a second, ugp-dependent transport system for sn-glycerol-3-phosphate that was derepressed by phosphate starvation. A S. typhimurium DNA bank containing EcoRI restriction fragments in phage lambda gt7 was used to clone the glpT gene in E. coli. Lysogens that were fully active in the transport of sn-glycerol-3-phosphate with a Km of 33 microM and a Vmax of 2.0 nmol/min . 10(8) cells were isolated in a delta glpT mutant of E. coli. The EcoRI fragment harboring glpT was 3.5 kilobases long and carried only part of glpQ, a gene distal to glpT but on the same operon. The fragment was subcloned in multicopy plasmid pACYC184. Strains carrying this hybrid plasmid produced large amounts of cytoplasmic membrane protein with an apparent molecular weight of 33,000, which was identified as the sn-glycerol-3-phosphate permease. Its properties were similar to the corresponding E. coli permease. The presence of the multicopy glpT hybrid plasmid had a strong influence on the synthesis or assembly of other cell envelope proteins of E. coli. For instance, the periplasmic ribose-binding protein was nearly absent. On the other hand, the quantity of an unidentified E. coli outer membrane protein usually present only in small amounts increased.

Glycolytic enzymes in the premolt field crab Paratelphusa hydrodromus (Milne-Edwards) (Crustacea)

The quantitative assay of hexokinase (HK), phosphorylase, phosphofructokinase (PFK), glucose 6-phosphate dehydrogenase (G-6-PDH), glycerol 3-phosphate dehydrogenase (G-3 PDH) and lactate dehydrogenase (LDH) revealed that coxal muscles compared to hepatopancreas contained higher activities of all the enzymes investigated. It appears that the coxal muscles of the premolt field crab has carbohydrate-based fuel economy. The hepatopancreas is a rich source of lipid and very poor source of glycogen. The activity of G-6-PDH is moderately high in the hepatopancreas. It seems that in this lipogenic tissue conversion of G-6-P to triose phosphate occurs predominately via pentose-phosphate pathway thus generating NADPH for lipogenesis. The relative G-3PDH ad LDH activities in hepatopancreas and coxal muscles led us to believe that the reconversion of NAD from NADH in hepatopancreas nd muscle flexor is effected by glycerol 3-phosphate shuttle, whereas in muscle extensor it is achieved by both G-3PDH and LDH activities.

Interaction of the dissociable glycerol-3-phosphate dehydrogenase and fructose-1,6-bisphosphate aldolase. Quantitative analysis by an extrinsic fluorescence probe

Cytoplasmic sn-glycerol-3-phosphate dehydrogenase, labelled covalently with fluorescein isothiocyanate, shows an enzyme-concentration-dependent fluorescence anisotropy. The anisotropy versus enzyme concentration curve is shifted towards higher concentrations when substrates are present. The comparison of the dissociation constants estimated from anisotropy measurements and derived from kinetic experiments suggests that the substrate-induced dissociation of the dimeric dehydrogenase is slow with respect to the enzymatic reaction catalyzed by either its monomeric or dimeric form. The fluorescence anisotropy of the fluorescent dye-labelled dehydrogenase increase with time upon addition of unlabelled fructose-1,6-bisphosphate aldolase approaching a limiting value. This fact indicates the binding of fructose-1,6-bisphosphate aldolase aldose aldolase to glycerolphosphate dehydrogenase. A model is proposed assuming simultaneous binding of tetrameric fructose-1,6-bisphosphate aldolase to monomeric and dimeric glycerolphosphate dehydrogenase with 1:1 stoichiometry. The dissociation constants, as parameters fitted to the experimental curves, were estimated as 0.2 microM and 1 microM for aldolase-dimeric-glycerolphosphate-dehydrogenase and aldolase-monomeric-glycerolphosphate-dehydrogenase complexes respectively.

Tissue effects of iron deficiency in the rat

Measurements of succinate dehydrogenase and mitochondrial glycerol-3-phosphate dehydrogenase activities, iron, cytochrome c and myoglobin, were made on various hind-leg muscles, fast-twitch red and white muscle and heart and liver of male Wistar rats fed an iron-deficient diet on weaning. Rats fed the same diet and given 20 mg iron intraperitoneally as iron-dextran (Imferon) served as controls. For iron-repletion studies anemic rats (hemoglobin less than 7 g/dl) were given a single injection of 10 mg iron (Imferon) and the time course of change in the above parameters was followed up to 22 days after injection. The iron concentration of most iron-deficient muscles dropped to approx. 35% of control, the heart to 60% and liver to 13%. On repletion, the iron concentration of all tissues increase significantly by 4 days. While the levels of cytochrome c and myoglobin approximated the iron levels in muscle, they did not change significantly in the heart. Succinate dehydrogenase activity dropped profoundly in muscle, to 10-30% of control; on repletion, the activity increased significantly. Mitochondrial glycerol-3-phosphate dehydrogenase activity showed only small changes in iron-deficient tissues.

Differentiation under the control of insulin of rat preadipocytes in primary culture. Isolation of homogeneous cellular fractions by gradient centrifugation

Using a density gradient medium (Percoll) we succeeded in isolating homogeneous cell populations from the stromal-vascular fraction of the inguinal tissue of 3-day-old rats. In primary culture, in medium 199 supplemented with 10% fetal calf serum and 5.5 mM glucose, almost complete differentiation (90%) of these fractions was obtained for the first time in presence of a physiological concentration of insulin (10(-9) M). During the adipose conversion, insulin markedly enhanced the activities of glycerol-3-phosphate dehydrogenase and acid: CoA ligase. When VLDL and heparin were added with insulin to the medium, this effect was not potentiated. On the contrary, VLDL and heparin in presence of insulin increased the triglyceride content of the cells. With VLDL and heparin only, the biochemical and morphological characteristics of the cells were very similar to those observed in control culture. The heavier fraction was morphologically heterogeneous and did not undergo the adipose conversion to the same extent as the two lighter fractions. It was concluded that this model could be helpful in studying the proliferation and the differentiation of preadipocytes at an early stage of development.