K(+)-p-nitrophenylphosphatase activity in rat brain and liver.

K(+)-p-nitrophenylphosphatase (K(+)pNPPase) is the enzyme, which is considered to be involved in K(+)-dependent hydrolysis of the phosphoenzyme in the reaction cycle of Na(+), K(+)ATPase. The aim of our present study was to characterize some features of K(+)pNPPase in homogenates of the rat brain and liver. We determined p-nitrophenylphosphatase (pNPPase) activity in the presence of various ion combinations (Mg(2+)+ K(+), Mg(2+), K(+)). We found a higher total pNPPase activity in the brain (0.8+/-0.079 nkat/mg protein) than in the liver (0.08+/-0.01 nkat/mg protein). Contrary to the liver, the main part of the total brain activity was K(+)-dependent. The activity of K(+)pNPPase was significantly higher in cerebral cortex homogenates (0.86+/-0.073 nkat/mg protein) in comparison to those of the whole brain (0.57+/-0.075 nkat/mg protein). The specific K(+)pNPPase activity was two times higher in the isolated pellet fraction (0.911+/-0.07 nkat/mg protein), rich in synaptosomes, compared to the whole brain homogenate (0.57+/-0.075 nkat/mg protein). Our results demonstrate the high activity of K(+)pNPPase in the brain tissue and its distribution mainly into the pellet fraction, what might indicate a possible role of K(+)pNPPase in specific structures of the brain, e.g. in synaptosomes.

Relationship between the structure of carbonylcyanide phenylhydrazones and inhibition of growth of microorganisms, stimulation of respiration of yeast cells and rat liver mitochondria.

The effect of ten derivatives of carbonylcyanide phenylhydrazone on growth of bacteria, yeast and different species of filamentous fungi was investigated. In yeast and mitochondria isolated from rat liver the effect of these derivatives on the respiratory activity was also followed. The relative efficiency of the individual derivatives of carbonylcyanide phenylhydrazone was determined on the basis of the results obtained. It was shown that derivatives, in which the substituent on the benzene ring causes simultaneously an increase of acidity and lipophilicity of the derivative as compared with the non-substituted carbonylcyanide phenylhydrazone (4-trifluoromethoxy-, 3-chloro-, 4-chloro and 3,4-dichloro-derivatives) were most effective.