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[Physico-chemical properties of specific protein kinases during intensification of lipogenesis and treatment with nicotinic acid].

Protein kinase strong-associated with acetyl-CoA-carboxylase is isolated from the liver of chicken and 300-fold purified with alimentary intensification of lipogenesis and under the effect of nicotinic acid against this background. The obtained enzymes are studied comparatively. It is found that their preparations are phosphorylated with different rate, have two pH optima and differ in the sensitivity to cAMP and to thermostable protein inhibitor. The hydrophobic chromatography was used to separate components of the acetyl-CoA-carboxylase-protein kinase complex and to reveal in the chicken liver cAMP-dependent and cAMP-independent protein kinases highly specific to acetyl-CoA-carboxylase and strongly bound with it.

Acetyl-CoA Carboxylase↗

Kinetic properties of nicotinic acid adenine dinucleotide phosphate-induced Ca2+ release.

Three endogenous molecules have now been shown to release Ca2+ in the sea urchin egg: inositol trisphosphate (InsP3), cyclic adenosine 5'-diphosphate ribose (cADPR), and nicotinic acid adenine dinucleotide phosphate (NAADP), a derivative of NADP. While the mechanism through which the first two molecules are able to release Ca2+ is established and well characterized with InsP3 and cADPR-activating InsP3 and ryanodine receptors, respectively, the newly described NAADP has been shown to release Ca2+ via an entirely different mechanism. The most striking feature of this novel Ca2+ release mechanism is its inactivation, since subthreshold concentrations of NAADP are able to fully and irreversibly desensitize the channel. In the present study we have investigated the fast kinetics of activation and inactivation of NAADP-induced Ca2+ release. NAADP was found to release Ca2+ in a biphasic manner, and such release was preceded by a pronounced latent period, which was inversely dependent on concentration. Moreover, the kinetic features of NAADP-induced Ca2+ release were not altered by pretreatment with low concentrations of NAADP, although the extent of Ca2+ release was greatly affected. Our data suggest that the inactivation of NAADP-induced Ca2+ release is an all-or-none phenomenon, and while some receptors have been fully inactivated, those that remain sensitive to NAADP do so without any change in kinetic features.

Animals↗

Nicotinic acid phosphoribosyltransferase activity in human erythrocytes: studies using a new HPLC method.

A non-radiochemical method linked to reverse-phase high-performance liquid chromatography was developed to determine the activity of nicotinic acid phosphoribosyltransferase (EC 2.4.2.11) in crude lysates of human red blood cells. The method is accurate and easily reproducible in different chromatographic systems. The enzyme activity was determined in erythrocytes of healthy subjects and in patients with different purine disorders showing altered NAD levels. Very low enzyme activity was found in a boy hemizygous for phosphoribosylpyrophosphate synthetase superactivity, consistent with the low erythrocyte NAD concentration.

Adenine Phosphoribosyltransferase↗