Vmax Values Of Enzyme Research Articles

Temperature acclimation and adaptation of enzyme physiology in Neurospora discreta

Abstract Fungal metabolic rates could increase under climate warming but may be counteracted by mechanisms of physiological acclimation and evolutionary adaptation. We hypothesized that Vmax and Km parameters of Neurospora discreta extracellular enzymes would acclimate to warmer temperatures through compensatory mechanisms. We also predicted that evolution under warmer temperatures would alter enzyme parameters and fungal respiration through adaptive mechanisms. In contrast to these predictions, growth at higher temperature (22 °C versus 16 °C) increased the temperature-corrected Vmax of three enzymes. The carbon substrate used for fungal growth (lignin versus sucrose) had a much greater impact on enzyme Vmax than temperature. Following experimental evolution, the enzymatic parameters of Neurospora strains did not adapt to higher temperatures as hypothesized; rather, enzyme Vmax values were unaffected, and respiration rates increased. Together, these results suggest that physiological and evolutionary mechanisms are unlikely to counteract soil carbon losses driven by saprotrophic fungi under climate warming.

Isolation of lipase producing thermophilic bacteria: Optimization of production and reaction conditions for lipase from Geobacillus sp.

Lipases catalyze the hydrolysis and the synthesis of esters formed from glycerol and long chain fatty acids. Lipases occur widely in nature, but only microbial lipases are commercially significant. In the present study, thirty-two bacterial strains, isolated from soil sample of a hot spring were screened for lipase production. The strain TS-4, which gave maximum activity, was identified as Geobacillus sp. at MTCC, IMTECH, Chandigarh. The isolated lipase producing bacteria were grown on minimal salt medium containing olive oil. Maximal quantities of lipase were produced when 30 h old inoculum was used at 10% (v/v) in production medium and incubated in shaking conditions (150 rpm) for 72 h. The optimal temperature and pH for the bacterial growth and lipase production were found to be 60°C and 9.5, respectively. Maximal enzyme production resulted when mustard oil was used as carbon source and yeast extract as sole nitrogen source at a concentration of 1% (v/v) and 0.15% (w/v), respectively. The different optimized reaction parameters were temperature 65°C, pH 8.5, incubation time 10 min and substrate p-nitrophenyl palmitate. The Km and Vmax values of enzyme were found to be 14 mM and 17.86 μmol ml-1min-1, respectively, with p-nitrophenyl palmitate as substrate. All metal ions studied (1 mM) increased the lipase activity.

Thyroid hormone controls carnitine status through modifications of gamma-butyrobetaine hydroxylase activity and gene expression.

The carnitine system plays a key role in beta-oxidation of long-chain fatty acids by permitting their transport into the mitochondrial matrix. The effects of hypothyroidism and hyperthyroidism were studied on gamma-butyrobetaine hydroxylase (BBH), the enzyme responsible for carnitine biosynthesis in the rat. In rat liver, BBH activity was decreased in the hypothyroid state and increased in hyperthyroid animals. The modifications in BBH activity correlated with changes in the enzyme Vmax values. These changes were shown to be related to hepatic BBH mRNA abundance. Thyroid hormones are known to interact with lipid metabolism, in particular by increasing long-chain fatty acid oxidation through activation of carnitine-dependent fatty acid import into mitochondria. Our study showed that thyroid hormones also increased carnitine bioavailability.

Salicylate and Mitochondrial Monoamine Oxidase Function in Reye's Syndrome

The main objective of this investigation was to study the effect of salicylate on platelet mitochondrial monoamine oxidase (MAO) activity isolated frrom blood of two patients with Reye's syndrome. Comparative studies were made with hospitalized children without Reye's syndrome (n=27) and healthy children (n=19) serving as controls. Platelet MAO was measured by a radioenzymatic technique with [14C]tyramine as a substrate. The results of this study showed that salicylate (1.0mM) caused an appreciable inhibition of the platelet MAO activity of patients with Reye's syndrome at the onset of the illness. This was demonstrated by a >50% reduction in enzyme maximum velocity (Vmax) value. The salicylate MAO-inhibitory effect was maintained throughout the duration of the illness. Salicylate had only a minimal MAO-inhibitory effect on platelets isolated from blood of recovered Reye's syndrome patients, healthy controls, and non-Reye's hospitalized children, and no apparent effect on enzyme Vmax values. These preliminary findings suggest that salicylate-induced mitochondrial injury may affect MAO function in children with Reye's syndrome.