Carbohydrate oxidation by leucoplasts from suspension cultures of soybean (Glycine max L.)

The aim of this work was to discover how leucoplasts from suspension cultures of soybean (Glycine max L.) oxidize hexose monophosphates. Leucoplasts were isolated from protoplast lysates on a continuous gradient of Nycodenz with a yield of 28% and an intactness of 80%. Incubation of the leucoplasts with ¹⁴C-labelled substrates led to ¹⁴CO₂ production, that was dependent upon leucoplast intactness, from [U-¹⁴C]glucose 6-phosphate, [U-¹⁴C]glucose 1-phosphate, [U-¹⁴C] fructose 6-phosphate and [U-¹⁴C]glucose+ATP, but not from [U-¹⁴C]fructose-1,6-bisphosphate or [U-¹⁴C]triose phosphate. The yield from [U-¹⁴C]glucose 6-phosphate was at least four times greater than that from any of the other substrates. When [1-¹⁴C]-, [2-¹⁴C]-, [3,4-¹⁴C]-, and [6-¹⁴C]glucose 6-phosphate were supplied to leucoplasts significant ¹⁴CO₂ production that was dependent upon leucoplast intactness was found only for [1-¹⁴C]glucose 6-phosphate. It is argued that soybean cell leucoplasts oxidize glucose 6-phosphate via the oxidative pentose phosphate pathway with very little recycling, and that in these plastids glycolysis to acetyl CoA is negligible.S.A.C. thanks the Science and Engineering Research Council for a research studentship.     

Energy metabolism in hypoxic astrocytes: Protective mechanism of fructose-1,6-bisphosphate

The protective effects of fructose-1,6-biphosphate (FBP) during hypoxia/ischemia are thought to result from uptake and utilization of FBP as a substrate for glycolysis or from stimulation of glucose metabolism. To test these hypotheses, we measumed CO₂ and lactate production from [6-¹⁴C]glucose, [1-¹⁴C]glucose, and [U-¹⁴C]FBP in normoxic and hypoxic cultured astrocytes with and without FBP present. FBP had little effect on CO₂ production by glycolysis, but increased CO₂ production by the pentose phosphate pathway. Labeled FBP produced very small amounts of CO₂. Lactate production from [1-, and 6-¹⁴C]glucose increased similarly during hypoxic hypoxia; the increase was independent of added FBP. Labeled lactate from [U-¹⁴C]FBP was minimal. We conclude that exogenous FBP is not used by astrocytes as a substrate for glycolysis and that FBP alters glucose metabolism.     

Metabolic Interactions Between Glucose, Glycerol, Alanine and Acetate in Leishmania braziliensis panamensis Promastigotes

¹³C-nuciear magnetic resonance (NMR) spectroscopy was used to investigate the products of glycerol and acetate metabolism released by Leishmania braziliensis panamensis promastigotes and also to examine the interaction of each of these substrates with glucose or alanine. The NMR data were supplemented by measurements of the rates of oxygen consumption and substrate utilization, and of ¹⁴CO₂ production from ¹⁴C-labeIed substrate. Cells incubated with [2-¹³C]glycerol released acetate, succinate and D-lactate in addition to CO₂. Cells incubated with acetate released only CO₂. More succinate C-2/C-3 than C-l/C-4 was released from both [2-¹³C]glycerol and [2-¹³C]glucose, indicating that succinate was formed predominantly by CO₂ fixation followed by reverse flux through part of the Krebs cycle. Some redistribution of the position of labeling was also seen in alanine and pyruvate, suggesting cycling through pyruvate/oxaloacetate/phosphoenolpyruvate. Cells incubated with combinations of 2 substrates consumed oxygen at the same rate as cells incubated with 1 or no substrate, even though the total substrate utilization had increased. When promastigotes were incubated with both glycerol and glucose, the rate of glucose consumption was unchanged but glycerol consumption decreased about 50%, and the rate of ¹⁴CO₂ production from [l,(3)-¹⁴C]glycerol decreased about 60%. Alanine did not affect the rates of consumption of glucose or glycerol, but decreased ¹⁴CO₂ production from these substrates by increasing flow of label into alanine. Although glucose decreased alanine consumption by 70%, it increased the rate of ¹⁴CO₂ production from [U-¹⁴C]- and [l-¹⁴C]alanine by about 20%. This is consistent with rapid equilibration of alanine with pyruvate derived from glucose and yet little decrease in the specific activity of the large alanine pool.     

THE HEXOSE MONOPHOSPHATE PATHWAY IN ETHYLNITROSOUREA INDUCED TUMORS OF THE NERVOUS SYSTEM

Respiration studies in vitro, in which tissue slices were incubated with [1-¹⁴C]glucose or [6-¹⁴C]glucose and ¹⁴CO₂ collected, resulted in C-1/C-6 ¹⁴CO₂ ratios that were higher in slices of tumor and newborn brain than in slices of adult brain. In adult brain, the C-1/C-6 ¹⁴CO₂ ratio averaged close to unity. In slices of tumor and newborn brain however, the mean C-1/C-6 ratio was greater than three. Addition of phenazine methosulfate (PMS) increased conversion of [1-¹⁴C]glucose to ¹⁴CO₂ in slices of normal adult brain 5-fold, and in slices of newborn brain and tumor, approx 12-fold. Injection of animals with 6-aminonicotinamide (6-AN) decreased conversion of [1-¹⁴C]glucose in slices of normal brain 30% but decreased conversion in tumor slices by 80%. Evidence supports the presence of an active hexose monophosphate pathway (HMP) in tumors of the nervous system regulated in part by available NADP⁺ levels. Inhibition by 6-AN was more effective in tumors than in normal adult brain.     

Oxidation of Glucose,Ribose, Alanine,and Glutamate by Leishmania braziliensis panamensis1

The metabolism of [1-¹⁴C]- and [6-¹⁴C]glucose, [1-¹⁴]ribose, [1-¹⁴C]- and [U-¹⁴C]alanine, and [1-¹⁴C]- and [5-¹⁴C]glutamate by the promastigotes of Leishmania braziliensis panamensis was investigated in cells resuspended in Hanks' balanced salt solution supplemented with ribose, alanine, or glutamate. The ratio of ¹⁴CO₂ produced from [1-¹⁴C]glucose to that from [6-¹⁴C]glucose ranged from about two to six, indicating appreciable carbon flow through the pentose phosphate pathway. A functional pentose phosphate pathway was further demonstrated by the production of ¹⁴CO₂ from [1-¹⁴C]ribose although the rate of ribose oxidation was much lower than the rate of glucose oxidation. The rate of ¹⁴CO₂ production from [1-¹⁴C]glucose was almost linear with time of incubation, whereas that of [6-¹⁴C]glucose accelerated, consistent with an increasing rate of flux through the Embden-Meyerhof pathway during incubation. Increasing the assay temperature from 26°C to 34°C had no appreciable effect on the rates or time courses of oxidation of either [1-¹⁴C]- or [6-¹⁴C]glucose or of [1-¹⁴C]ribose. Both alanine and glutamate were oxidized by L. b. panamensis, and at rates comparable to or appreciably greater than the rate of oxidation of glucose. The ratios of ¹⁴CO₂ produced from [1-¹⁴C]- to [U-¹⁴C]alanine and from [1-¹⁴C]- to [5^-14C]glutamate indicated that these compounds were metabolized via a functioning tricarboxylic acid cycle and that most of the label that entered the tricarboxylic acid cycle was oxidized to carbon dioxide. Heating the cultures for 6 or 12 h at 34°C, which converts the promastigotes into an ellipsoidally shaped intermediate form, decreased the rates of oxidation of glucose, alanine, and glutamate. The oxidation of glutamate decreased by about 50% and 70% after a 6-h or 12-h heat treatment, respectively. Returning the heated cultures to 26°C initiated a reversion to the promastigote form and recovery of the rate of glucose oxidation, but glutamate oxidation did not return to control levels by 19 h at 26°C.     

Glucose handling by hepatocytes from obese Zucker rats

Hepatocytes isolated from obese Zucker rats showed a significantly higher rate of both [U-¹⁴C]glucose and [U-¹⁴C]lactate incorporation into [¹⁴C]lipid than those from their lean counterparts. This was associated with a marked increase in the lipogenic rate measured by the incorporation of³H₂O into the cell esterified fatty acids. Although there were no changes in the incorporation of the tracer into either [¹⁴C]glycogen or¹⁴CO₂, the [¹⁴C] total uptake was significantly higher in the obese animals. The high rate of [¹⁴C]lipid synthesis from glucose was observed both at 15 and 30 mM substrate concentrations and was linked to an enhanced uptake of the tracer into the cell as measured using the decarboxilation of [1-¹⁴C]glucose in the presence of phenazine methosulphate. The presence of insulin in the incubation medium had no effect on the uptake of glucose by the liver cells. However, the large uptake of glucose by the hepatocytes from the obese animals was not related to an enhanced rate of transport as measured using 3-O-methyl[U-¹⁴C]glucose. The activity of glucose-6-phosphate dehydrogenase together with a higher [1-¹⁴C]glucose/[U-¹⁴C]glucose descarboxylation ratio indicate a predominant very active pentose phosphate pathway which may be responsible for the enhanced glucose uptake observed in the hepatocytes from the obese animals.     

Inhibition of glucose utilization for acetylcholine synthesis by cerebrospinal fluid.

Abstract— Replacement of bicarbonate-Locke incubation medium with feline CSF reduced [¹⁴C]ACh formation from [U-¹⁴C]glucose by rat brain mince approx 30%. CSF was obtained from a cannula leading to the cisterna magna of freely moving cats. The component of CSF responsible for inhibition was characterized as a dialyzable heat-stable organic anion. Choline acetyltransferase activity was not altered by CSF. [¹⁴C]ACh synthesis and ¹⁴CO₂ production from [U-¹⁴C]glucose but not from [2-¹⁴C]-pyruvate were inhibited by CSF, suggesting inhibition in the metabolism of glucose to pyruvate. The anionic fraction of human CSF was as potent as that from feline CSF in inhibiting ¹⁴CO₂ production from [U-¹⁴C]glucose. Brain hexokinase was inhibited by the anionic fraction of feline CSF. The inhibition was non-competitive with respect to glucose and uncompetitive with respect to ATP. It is suggested that inhibition of hexokinase by CSF was responsible at least in part for the inhibition of glucose metabolism which resulted in decreased [¹⁴C]ACh synthesis and ¹⁴CO₂ production.     

Effect of 2-deoxy-d-Glucose on Aminoacids Metabolism in Rats’ Cerebral Cortex Slices

We studied the effect of different concentrations of 2-deoxy-d-glucose on the l-[U-¹⁴C]leucine, l-[1-¹⁴C]leucine and [1-¹⁴C]glycine metabolism in slices of cerebral cortex of 10-day-old rats. 2-deoxy-d-glucose since 0.5 mM concentration has inhibited significantly the protein synthesis from l-[U-¹⁴C]leucine and from [1-¹⁴C]glycine in relation to the medium containing only Krebs Ringer bicarbonate. Potassium 8.0 mM in incubation medium did not stimulate the protein synthesis compared to the medium containing 2.7 mM, and at 50 mM diminishes more than 2.5 times the protein synthesis compared to the other concentration. Only at the concentration of 5.0 mM, 2-deoxy-d-glucose inhibited the CO₂ production and lipid synthesis from l-[U-¹⁴C] leucine. This compound did not inhibit either CO₂ production, or lipid synthesis from [1-¹⁴C]glycine. Lactate at 10 mM and glucose 5.0 mM did not revert the inhibitory effect of 2-deoxy-d-glucose on the protein synthesis from l-[U-¹⁴C]leucine. 2-deoxy-d-glucose at 2.0 mM did not show any effect either on CO₂ production, or on lipid synthesis from l-[U-¹⁴C]lactate 10 mM and glucose 5.0 mM.     

Acetylcholine Synthesis and CO2 Production from Variously Labeled Glucose in Rat Brain Slices and Synaptosomes

Abstract: The molecular basis of the close linkage between oxidative metabolism and acetylcholine (ACh) synthesis is still unclear. We studied this problem in slices and synaptosomes by measurement of ACh synthesis from [U-¹⁴C]glucose, and ¹⁴CO₂ production from [3,4-¹⁴C]- and [2-¹⁴C]glucose, an index of glucose decarboxylation by the pyruvate dehydrogenase complex (PDH) and the enzymes of the Krebs cycle, respectively. We examined both under conditions that either inhibited (low O₂ or antimycin) or stimulated (2,4- dinitrophenol [DNP] or 35 mm -K⁺) ¹⁴CO₂ production from [2-¹⁴C]- or [3,4-¹⁴C]glucose. Incorporation of [U-¹⁴C]glucose into ACh was reduced under low O₂ and by antimycin or DNP (by 51-93%) and stimulated by 35 mm -K⁺ (by 30-60%). Under all of these conditions, ACh synthesis and the decarboxylation of [3,4-¹⁴C]- and [2-¹⁴C]glucose were linearly related (r= 0.741 and 0.579, respectively). The difference in the rate of ¹⁴CO₂ production from [3,4-¹⁴C]- and [2-¹⁴C]glucose was used as a measure of the amount of glucose that was not oxidatively decarboxylated (efflux). We found that efflux was reduced (low 0₂ and antimycin), unchanged (DNP in slices), or increased (DNP in synaptosomes and K⁺ stimulation in slices) compared with control values under 100% O₂. ACh synthesis and efflux were more closely related (r= 0.860) than ACh synthesis and ¹⁴CO₂ production from variously labeled glucoses.     

Biosynthesis of securinine,the main alkaloid of Securinega suffruticosa

Biosynthesis of securinine was studied by incorporation experiments in Securinega suffruticosa. Among presumed precursors tested, lysine, cadaverine, and tyrosine showed the highest incorporation into securinine. Degradation experiments revealed that cadaverine-[1,5-¹⁴C] labelled specifically the piperidine ring of securinine and the radioactivity from dl-tyrosine-[2-¹⁴C] was introduced into the C-11 lactone carbonyl. Experiments with L-tyrosine-[U-¹⁴C] and L-tyrosine-[3′,5′-³H; U-¹⁴C] prove that the remaining C₆Sz.sbnd;C₂ moiety is derived from the aromatic ring and the C-2 and C-3 or tyrosine.     

THE METABOLISM OF LEUCINE BY DEVELOPING RAT BRAIN: EFFECT OF LEUCINE AND 2-OXO-4-METHYLVALERATE ON LIPID SYNTHESIS FROM GLUCOSE AND KETONE BODIES

Abstract— The oxidation of l -[U-¹⁴C]leucine and l -[l-¹⁴C]leucine at varying concentrations from 0.1 to 5mM to CO₂ and the incorporation into cerebral lipids and proteins by brain slices from 1-week old rats were markedly stimulated by glucose. Although the addition of S mM-dl -3-hydroxybutyrate had no effect on the metabolism of [U-¹⁴C]leucine by brain slices from suckling rats, the stimulatory effects of glucose on the metabolism of l -[U-¹⁴C]leucine were markedly reduced in the presence of dl -3-hydroxybutyrate. The stimulatory effect of glucose on leucine oxidation was, however, not observed in adult rat brain. Furthermore, the incorporation of leucine-carbon into cerebral lipids and proteins was also very low in the adult brain. The incorporation of l -[U-¹⁴C]leucine into cerebral lipids by cortex slices was higher during the first 2 postnatal weeks, which then declined to the adult level. During this time span, the oxidation of l -[U-¹⁴C]leucine to CO₂ remained relatively unchanged. The incorporation in vivo of D-3-hydroxy[3-¹⁴C]butyrate into cerebral lipids was markedly decreased by acute hyperleucinemia induced by injecting leucine into 9-day old rats. In in vitro experiments, 5 mM-leucine had no effect on the oxidation of [U-¹⁴C]glucose to CO₂ or its incorporation into lipids by brain slices from 1-week old rats. However, 5 mM-leucine inhibited the oxidation of d -3-hydroxy-[3-¹⁴C]butyrate, [3-¹⁴C]acetoacetate and [1-¹⁴C]acetate to CO₂ by brain slices, but their incorporation into cerebral lipids was not affected by leucine. In contrast 2-oxo-4-methylvalerate, a deaminated metabolite of leucine, markedly inhibited both the oxidation to CO₂ and the incorporation into lipids of labelled glucose, ketone bodies and acetate by cortex slices from 1-week old rats. These findings suggest that the reduction in the incorporation in vivo of d -3-hydroxy[3-¹⁴C]butyrate into cerebral lipids in rats injected with leucine is most likely caused by 2-oxo-4-methylvalerate formed from leucine. Since the concentrations of leucine and 2-oxo-4-methylvalerate in plasma of untreated patients with maple-syrup urine disease are markedly elevated, our findings are compatible with the possibility that an alteration in the metabolism of glucose and ketone bodies in the brain may contribute to the pathophysiology of this disease.     

A simple method for determining total glucose utilisation by isolated adipocytes using (5-3H)-glucose

Glucose utilisation by adipocytes incubated with and without insulin and at two concentrations of extracellular glucose has been estimated by three different procedures. Glucose disappearance from the medium was calculated by using glucose oxidase to determine the glucose concentration remaining after incubation and comparing this with the glucose concentration in standard solutions made up by appropriate dilution of the original medium. [U-¹⁴C]-glucose utilisation was calculated by summing the ¹⁴C found in CO₂, triglycerides, and anions. [³H]-H₂O formation from [5-³H]-glucose was the third measure of glucose utilisation. All three methods gave similar answers, but the [5-³H]-glucose is simpler to use than [U-¹⁴C]-glucose and gives substantially more reproducible results than glucose oxidase.     

Polyamines in Rice Seedlings under Oxygen-Deficit Stress

Incubation of 3-d-old seedlings of Oryza sativa L. cv Arborio under anaerobic conditions, leads to a large increase in the titer of free putrescine while aerobic incubation causes a slight decrease. After 2 days, the putrescine level is about 2.5 times greater without oxygen than in air. The rice coleoptile also accumulates a large amount of bound putrescine and, to a lesser extent, spermidine and spermine (mainly as acid-soluble conjugates). Accumulation of conjugates in the roots is severely inhibited by the anaerobic treatment. Feeding experiments with labeled amino acids showed that anoxia stimulates the release of ¹⁴CO₂ from tissues fed with [¹⁴C]arginine and that arginine is the precursor in putrescine biosynthesis. After 2 d of anoxia, the activity of arginine decarboxylase was 42% and 89% greater in coleoptile and root, respectively, than in the aerobic condition. The causes of the differences in polyamine metabolism in anoxic coleoptiles and roots are discussed.     

The effect of methionine on the metabolism of serine and glycine in vitamin B-12-deficient rats

The effect of methionine supplementation on glycine and serine metabolism was studied in vitamin B-12-deficient rats which received only 0.2% methionine in the diet. In the perfused liver, incorporation of the C-2 of glycine to the C-3 of serine was increased by addition of methionine to the perfusate. The oxidation of [1-¹⁴C]glycine to ¹⁴CO₂ was however depressed. Unlike methionine, glycine did not have any significant effect on the liver folate coenzyme distribution. Oxidation of [3-¹⁴C]serine to ¹⁴CO₂ both in vivo and in perfused liver was increased by methionine. A major portion of the C-3 radioactivity however was recovered in glucose. Data presented indicate that the rate of oxidation of [2-¹⁴C]histidine to ¹⁴CO₂ is more sensitive indicator of folate deficiency than the rate of oxidation of [3-¹⁴C] serine to ¹⁴CO₂ although both are presumably tetrahydrofolate dependent.     

Metabolic Response to Nonglucidic Nutrient Secretagogues and Enzymatic Activities in Pancreatic Islets of Adult Rats after Neonatal Streptozotocin Administration

In islets from adult rats injected with streptozotocin during the neonatal period, both a nonmetabolized analog of L-leucine and 3-phenylpyruvate augmented ¹⁴CO₂ output from islets either prelabeled with L-[U-¹⁴C]glutamine or exposed to D-[2-¹⁴C]glucose and D-[6-¹⁴C]glucose in a manner qualitatively comparable to that found in islets from control rats. The islets of diabetic rats differed, however, from those of control rats by their unresponsiveness to both the L-leucine analog and a high concentration of D-glucose in terms of increasing ³HOH generation from [2-³H]glycerol, an impaired sparing action of the hexose upon ¹⁴CO₂ output from islets prelabeled with [U-¹⁴C]palmitate, and, most importantly, by a decreased rate of D-[2-¹⁴C]glucose and D-[6-¹⁴C]glucose oxidation when either incubated at a high concentration of the hexose (16.7 mM) or stimulated by nonglucidic nutrient secretagogues at a low concentration of D-glucose (2.8 mM). In islet homogenates, the activity of glyceraldehyde phosphate dehydrogenase, glutamate decarboxylase, and NADP-malate dehydrogenase was lower in diabetic than control islets. Such was not the case for glutamatealanine transaminase, glutamate-aspartate transaminase, or glutamate dehydrogenase. The neonatal injection of streptozotocin thus affected, in the adult rats, the activity of several islet enzymes. Nevertheless, the metabolic data suggest that an impaired circulation in the glycerol phosphate shuttle, as observed in response to stimulation of the islets by either a high concentration of D-glucose or nonglucidic nutrient secretagogues, represents an essential determinant of the preferential impairment of glucose-induced insulin release in this model of non-insulin-dependent diabetes.     

Diurnal change of tartrate dissimilation during the ripening of grapes

l(+)-tartrate-[U-¹⁴C] or sucrose-[U-¹⁴C] was fed into grape berries and ¹⁴CO₂ evolution was determined. ¹⁴CO₂ evolution front l(+)-tartrate-[U-¹⁴C] was slightly higher in mature than immature berries, and that from sucrose-[U-¹⁴C] was higher in immature than mature ones. ¹⁴CO₂ evolution from l(+)-tartrate-[U-¹⁴C] was irregular throughout the day until 2 or 3 weeks after flowering. This stage shifted to regular ¹⁴CO₂ evolution until 6 or 7 weeks after flowering, and the mode of ¹⁴CO₂ evolution showed diurnal variation; higher in the day than at night. Then the stage without variation of ¹⁴CO₂ evolution followed 10 weeks after flowering. These observations indicate that tartrate is not biochemically inert in grape berries, while the amount of ¹⁴CO₂ evolution from sucrose-[U-¹⁴C] was higher at night than in the day through the whole ripening process, except in the early stage.     

Biochemical evidence for a secretory role of the pineal body. Oxidation of [1-14C]- and [6-14C]glucose in vitro by pineal body, pituitary, and brain from young and adult animals

The conversion of [1-¹⁴C] label from glucose to ¹⁴CO₂in vitro by bovine pineal bodies was 7-24 times as great as that of [6-¹⁴C]. These values for C-1/C-6 oxidation ratios are similar to those found for all known endocrine tissues and in contrast to those for brain which range from 1.0 to 1.4. Total glucose oxidation, both C-1 and C-6, and C-1/C-6 ratios were lower in pineal bodies from adult (3-8 years) than from young (5-10 months) animals. Total glucose oxidation by the posterior pituitary was lower in the adult than in the young, generally lower in the anterior pituitary of the adult, and higher in the brain of the adult. Epinephrine, 10^?4m , increased the oxidation by pineal tissue of [1-¹⁴C] by 170 per cent and of [6-¹⁴C] by 46 per cent. The relatively high C-1/C-6 ratios found for pineal tissue are indicative of an operative hexosemonophosphate pathway, which we have previously suggested to be correlated with hormone secretion and/or storage. The present findings provide biochemical support for the hypothesis that the pineal body has an endocrine function in mammals.     

GLUCOSE AND AMINO ACID METABOLISM IN OCTOPUS OPTIC AND VERTICAL LOBES IN VITRO

(1) The metabolism of glucose and amino acids in vitro was compared in the rat cerebral cortex and the optic and vertical lobes of the octopus brain. (2) Specific activities and pool sizes of the five amino acids, glutamate, aspartate, glutamine, alanine and γ-aminobutyric acid (GABA), were determined in octopus and rat brain slices after 2 hr incubation with 10 mm -[U-¹⁴C]glucose, 10 mm -L-[U-¹⁴C]glutamate, and 10mm -^L-[U-¹⁴C]glutamate with added 10 mM-glucose. Amino acid pool sizes were similar in rat and octopus brain, with the exception of alanine, which was higher in the octopus. Generally specific activities were from four- to 20-fold higher in rat brain. With [U-¹⁴C]glucose as substrate, specific activities of GABA and glutamate were highest in rat; those of alanine and glutamine highest in octopus brain. With ^L-[U-¹⁴C]glutamate the specific activities of GABA and aspartate were highest in rat, that of aspartate highest and GABA lowest in octopus. The addition of glucose to ^L-[U-¹⁴C]glutamate as substrate had little effect on the specific activities of any of the amino acids. (3) The uptake of some amino acids was determined by incubation with [U-¹⁴C]amino acids for 2 hr, and ¹⁴CO₂ formation was also measured. The amount of label taken up by octopus was uniformly 20-25 per cent of that found for rat brain. The amount of ¹⁴CO₂, however, differed according to the amino acid. Four times as much ¹⁴CO₂ was generated from alanine by octopus optic lobe and twice as much by the vertical lobe than rat cortex, but from glutamate, only 24 per cent in the optic and 15 per cent in the vertical lobe. No ¹⁴CO₂ was generated from [U-¹⁴C]GABA in the octopus, by contrast with the rat. (4) Activity of some of the enzymes involved in amino acid metabolism was determined in homogenates of rat cortex and octopus optic and vertical lobes, with and without activation by Triton X-100. Enzymic activities in the octopus, with the exception of alanine aminotransferase, were lower than in the rat, and glutamate decarboxylase could not be detected in octopus brain, in the absence of detergent.     

Glycine,Serine, and Leucine Metabolism in Different Regions of Rat Central Nervous System

We have investigated the glycine, serine and leucine metabolism in slices of various rat brain regions of 14-day-old or adult rats, using [1-¹⁴C]glycine, [2-¹⁴C]glycine, L-[3-¹⁴C]serine and L-[U-¹⁴C]leucine. We showed that the [1-¹⁴C]glycine oxidation to CO₂ in all regions studied occurs almost exclusively through its cleavage system (GCS) in brains of both 14-day-old and adults rats. In 14-day-old rats, the highest oxidation of [1-¹⁴C]glycine was in cerebellum and the lowest in medulla oblongata. In these animals, the L-[U-¹⁴C]leucine oxidation was lower than the [1-¹⁴C]glycine oxidation, except in medulla oblongata where both oxidations were the same. Serine was the amino acid that showed lowest oxidation to CO₂ in all structure studied. In adult rats brains, the highest oxidation of [1-¹⁴C]glycine was in cerebral cortex and the lowest in medulla oblongata. We have not seen difference in the lipid synthesis from both glycine labeled, neither in 14-day-old rats nor in adult ones, indicating that the lipids formed from glycine were not neutral. Lipid synthesis from serine was significantly high than lipid synthesis and from all other amino acids studied in all studied structures. Protein synthesis from L-[U-¹⁴C]leucine was significantly higher than that from glycine in all regions and ages studied.     

Comparison of oxidative metabolism in starved, fat-fed and carbohydrate-fed rats

1. Rats were starved for 48hr. or fed for 1 week on a high-fat or a high-carbohydrate diet. The effects of these dietary alterations on the rate of production of ¹⁴CO₂ from trace amounts of [U-¹⁴C]glucose, [1-¹⁴C]palmitate or [1-¹⁴C]acetate administered intravenously were studied. 2. The oxidation of [¹⁴C]glucose was most rapid in the carbohydrate-fed condition and was decreased significantly and to the same extent after starvation and after feeding with fat. 3. Under all dietary regimes studied the maximum rate of elimination of ¹⁴CO₂ from [¹⁴C]palmitate occurred within a few minutes after injection, but considerably more was oxidized after starvation and feeding with fat than after feeding with carbohydrate. 4. Alterations in diet had no effect on the oxidation and high recovery of administered [¹⁴C]acetate as ¹⁴CO₂. 5. Graphical analysis showed the presence of several exponential components in the ¹⁴CO₂-elimination curves. 6. In all studies a marked similarity in oxidative pattern was noted between the starved and the fat-fed rat.