Differential susceptibility to biological detergents of the particulate cGMP-stimulated phosphodiesterase from rat heart: preservation of the allosteric properties of the solubilized enzyme

The effects of various biological detergents on the particulate cGMP-stimulated cAMP phosphodiesterase activity from rat heart were investigated. When added to particulate fractions, anionic and non-ionic detergents diversely increased both cAMP and cGMP phosphodiesterase activities and slightly decreased the stimulatory effect of cGMP on cAMP hydrolysis whereas cationic detergents were rather inhibitory and drastically lowered the stimulatory effect of cGMP. Among the most efficient detergents, only sodium cholate was able to solubilize phosphodiesterase activity and preserve the stimulatory effect of cGMP on cAMP hydrolysis. Furthermore, the addition of glycerol significantly improved the conservation of the allosteric properties of the enzyme. Kinetic properties of the cholate-solubilized phosphodiesterase were quite identical to those of the membrane-bound enzyme.     

Retention of cryptic genes in microbial populations

Cryptic genes are silenced genes that can still be reactivated by mutation. Since they can make no positive contribution to the fitness of their carriers, it is not clear why many cryptic genes in microbial populations have not degenerated into useless DNA sequences. Hall et al. (1983) have suggested that cryptic genes have persisted because of occasional strong environmental selection for reactivated genes. The present mathematical study supports their suggestion. It shows that a cryptic gene can be retained without having any selective advantage over a useless DNA sequence, if selection for the reactivated gene occasionally occurs for a substantially long time.      

Age-related changes in arachidonic acid peroxidation and glutathione-peroxidase activity in human platelets.

Lipid peroxidation, vitamin E level and glutathione-peroxidase activity were determined in platelets from elderly (greater than 68 years) and young (21-43 years) people. To further assess the platelet lipid peroxidation, the metabolism of endogenous arachidonic acid in unstimulated platelets as well as that of the exogenous one were measured in the two groups. The oxygenated metabolites of arachidonic acid were enhanced in the elder population under both conditions tested. In addition, the platelet malondialdehyde content, a marker of the overall lipid peroxidation, was also found significantly increased in platelets from aged subjects. On the other hand, the platelet vitamin E level and the glutathione-peroxidase activity were significantly depressed in the elder group compared to the young one. These results suggest that the increased platelet activation observed with age could be linked to the accumulation of lipoxygenase-dependent peroxides associated with the decreased antioxidative defence of the cells, especially glutathione-peroxidase activity.