Kinetics of K(+)-p-nitrophenyl phosphatase stimulation by a brain soluble fraction.
We have already described the separation of two brain soluble fractions by Sephadex G-50, one of which stimulates (peak I) and the other inhibits (peak II) Na+, K(+)-ATPase and K(+)-p-nitrophenylphosphatase (K(+)-p-NPPase) activities. Here we examine the features of synaptosomal membrane p-NPPase activity in the presence and absence of brain peak I. It was observed that stimulation of Mg2+, K(+)-p-NPPase activity by peak I was concentration dependent. The ability of peak I to stimulate p-NPPase activity was lost by heat treatment followed by brief centrifugation. Pure serum albumin also stimulated enzyme activity. K(+)-p-NPPase stimulation by peak I proved dependent on K+ concentration but independent of Mg2+ and substrate p-nitrophenylphosphate concentrations. Since our determinations were performed in a non-phosphorylating condition reflecting the Na+, K(+)-ATPase Na+ site, it is suggested that peak I may stimulate the Na+-dependent enzyme phosphorylation known to take place from the internal cytoplasmic side.
Rodríguez de Lores Arnaiz
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Instituto de Biologia Cellular y Neurociencias Prof. Eduardo De Robertis, Facultad de Medicina, Universidad de Buenos Aires, Paraguay, Argentina.
D009597:4-Nitrophenylphosphatase / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000201:enzymology* / Q000648:ultrastructure*; D004795:Enzyme Stability; D005260:Female; D006358:Hot Temperature; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D013574:Synaptosomes / Q000201:enzymology
D009597:4-Nitrophenylphosphatase; D008274:Magnesium; D011188:Potassium