Studies on the mechanism of inhibition of growth of Vibrio cholerae by erythrose

Erythrose strongly inhibits the growth of Vibrio cholerae and Vibrio eltor. The inhibition can be reversed by washing the cells free from erythrose with sterile normal saline. The respiration of V. cholerae cells in the presence of glucose is markedly inhibited by erythrose but the oxygen uptake of cell-free extract under the same conditions is not affected. From the results of experiments on the uptake of [14C] glucose and [α-14C]methylglucoside, it may be concluded that erythrose inhibits the transport of glucose across the cell membrane and thereby inhibits the growth of the organism

Effect of erythropoietin on the peroxidase and tyrosine-iodinase activity of mouse thyroid and submaxillary gland

During an attempt to explore the mechanism of cobalt and vitamin B12 effect on the peroxidase and tyrosine iodinase activity, it was observed that cobalt and not vitamin B12in vivo elicits a high plasma titer of a humoral factor, erythropoietin, which caused increased 59Fe incorporation into red blood corpuscles. This erythropoietin was extracted from plasma or kidney and partially purified. This partially purified erythropoietin preparation when injected into starved rat caused increased 59Fe incorporation into red blood corpuscles. The potency of the partially purified erythropoietin preparation from plasma and kidney was compared. This partially purified erythropoietin, as well as sheep step-I erythropoietin, when administered to mice gave rise to a response almost similar to cobalt administration. It appears that the effect of cobalt on the peroxidase or tyrosine iodinase activity might be mediated through the elevation of the erythropoietin titer of plasma. Moreover, this erythropoietin was found to stimulate both peroxidase and tyrosine iodinase activity of the enzyme preparation of submaxillary gland in experiments in vitro. Erythropoietin, purified further in our laboratory, also produced the same effect. Neuraminidase-treated erythropoietin, in contrast, failed to execute any such stimulatory effect on the iodination of tyrosine

A comparative study of the peroxidases from thyroid glands of pigeon (Columba livia domestica) and common myna (Acridotheres tristis)

1. 1. The soluble supernatant fraction (105,000 g supernatant) of the pigeon and common myna thyroid gland showed high peroxidase activity. The peroxidase activity of the common myna was higher than that of the pigeon. 2. 2. The pH optimum of pigeon thyroid peroxidase was 5.5 whereas in the common myna it was 6.0. 3. 3. H2O2 (1.16 µmole/ml) was inhibitory to pigeon thyroid peroxidase whereas common myna thyroid peroxidase was not inhibited even at a concentration as high as 100 μmoles/ml. 4. 4. The effect of various inhibitors and stimulators on the peroxidase of the pigeon and common myna were studied and compared

Oxidation of 2,5-diketogluconate by a cell-free enzyme preparation from Acetobacter melanogenum

IT has been reported by Katznelson that 'old' intact cells and cell-free extracts of Acetobacter melanogenum oxidize glucose to gluconate, 2-ketogluconate and finally to 2,5-diketogluconate. We have obtained evidence that this last compound can be oxidized further

Effect of glucagon administration on mice liver fructose-1, 6-bisphosphatase

Intravenous administration of glucagon in mouse (200 μg/100 gm body wt), stimulated liver fructose-1,6-bisphosphatase at physiological pH by approximately 100% within 15 minutes. The stimulation was not due to protein synthesis. Similar stimulation was also observed on administration of cyclic AMP. Removal of the adrenal gland abolished the stimulatory effect of glucagon but not of cyclic AMP

Participation of an active glycolaldehyde-enzyme in the transketolase-catalyzed reaction

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Anaerobic formation of succinate from glucose and bicarbonate in resting cells of Leishmania donovani

The cell suspension of Leishmania donovani incorporates 14CO2 resulting in the formation of [14C]-succinic acid under anaerobic conditions. The results showed that the [14C]-succinate formation from [1-14C]-glucose is much greater than that from [6-14C]-glucose. [14C-pyruvate] takes part in the production of succinic acid under anaerobic conditions without decarboxylation. The anaerobic formation of succinate appears to involve the production of malate, which is then converted to succinate via the reduction of fumarate by the reversal of the tricarboxylic acid cycle. Evidence indicated that the active species in this carboxylation reaction was CO2 although HCO3 was active to some extent

Studies on malate or oxaloacetate formation from bicarbonate and pyruvate or phosphoenol pyruvate in cell-free extracts of Leishmania donovani

1. 1. Complete organization of the cell components was essential for succinate production, since the cell-free extract of Leishmania donovani could not produce succinate from PEP or pyruvate by carboxylation reaction. But it could effectively produce oxaloacetate or malate from PEP or pyruvate and bicarbonate. 2. 2. Studies with a cell-free extract of the organism further showed that at least three different carboxylating systems were present in the preparation of the organism. 3. 3. The activities of NADP-dependent malic enzyme, NADH-dependent malate dehydrogenase and fumarase were shown to be present in the cell-free extract of L. donovani

Effect of adrenergic agonists and antagonists on alanine amino transferase, fructose-1:6-bisphosphatase and glucose production in hepatocytes

Using rat hepatocytes we confirmed our previous results that glucagon and β-adrenergic agonists increased the enzyme activity of alanine aminotransferase (AAT) and propranolol abolished their effects. Only the enzyme activity was measured and other parameters like quantity of the enzyme or activation due to modification were not looked for. As in perfusion experiment phenylephrine and phenoxybenzamine (α-agonist and α-antagonist respectively) also increased the AAT activity in isolated rat hepatocytes and propranolol reversed these effects. The additive effect of glucagon and phenoxybenzamine on AAT was also persistant in hepatocyte system. Fructose- 1:6-bisphosphatase (Fru-P2ase), another key enzyme in gluconeogenic pathway, was elevated by glucagon and other β-adrenergic agonists both in liver perfusion and isolated hepatocyte experiments and was brought back to the normal level by propranolol. In this case also only the enzyme activity was measured and no other parameters were looked for. Unlike AAT this enzyme was not stimulated by phenylephrine or phenoxybenzamine. But AAT and Fru-P2-ase activities were increased significantly by adenylate cyclase activators like fluoride or forskolin. Thus, it appears that the regulation of fru-P2-ase by glucagon is purely a β-receptor mediated process whereas AAT activation shows a mixed type of regulation where some well known α-agonist and antagonists are behaving as β-agonists. Results further indicate the presence of phosphodiesterase in hepatocyte membrane which was stimulated by glucagon and brought back to the normal level by propranolol. The different adrenergic compounds stated above, not only modified the activity of the above two enzymes but also stimulated glucose production by hepatocytes from alanine which was in turn abolished by propranolol as well as amino oxyacetate (AOA), a highly specified inhibitor of AAT. This confirm the participation of AAT in gluconeogenesis from alanine in liver. Forskolin and fluoride also increased the glucose production from alanine and showed additive effects with glucagon, phenylephrine and phenoxybenzamine

Effect of glucagon and some other alpha and beta adrenergic agonists and antagonists on alanine amino transferase of perfused rat liver

Glucagon increased alanine amino transferase (AAT) activity in perfused rat liver by about 90% over control. Propranolol, the beta receptor antagonist, abolished the effect of glucagon on this enzyme. Well known beta receptor agonists like isoproterenol, norepinephrine and epinephrine also increased the enzyme activity under identical condition and the enhancement was similarly abolished by propranolol. These experiments suggest that the effect of glucagon on AAT was mediated through beta adrenergic receptor. However, the interesting observation was that phenylephrine, alpha receptor agonist and phenoxybenzamine and tolazoline, two alpha receptor antagonists, increased the AAT activity like glucagon in perfusion experiments and the effects of all these three agents were also abolished by propranolol. Glucagon, when perfused with phenoxybenzamine showed some additive effect. From all these results we are proposing that in our system phenoxybenzamine is acting as beta agonist although it is known to be an alpha antagonist