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Enzyme transfer of phosphate from adenosine triphosphate to protein-bound serine residues in cerebral microsomes.

ABSTRACT: 1. Microsomes from guinea-pig brain grey matter were incubated with [(32)P]ATP at 3mm concentration and the phosphate bound to the acid-washed, lipid-free residue was determined. 2. The binding process was Mg(2+)-dependent and resulted in the transfer of about 1-2 mmumoles of phosphate/mg. of protein/min. Under the conditions used univalent cations (Na(+),K(+) and Li(+)) inhibited the binding. 3. An unspecified proportion of this bound phosphate could be recovered in protein-derived phosphorylserine. The yield of labelled phosphorylserine was also decreased by univalent cations. 4. The bound phosphate formed with 3mm-MgATP was stable; addition of Na(+) or K(+) ions to the already labelled preparation had no effect on the bound phosphate level. 5. Bound phosphate was also formed when a solubilized fraction of the microsomes was incubated with ATP; univalent cations also inhibited this process. 6. p-Chloromercuribenzoate reduced the binding by about 25%; the inhibition was restored by cysteine.

SUBMITTER: Rodnight R

PROVIDER: S-EPMC1270133 | biostudies-other | 1966 Nov

REPOSITORIES: biostudies-other

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Project description:1. Microsomes prepared from guinea-pig and ox brain were incubated for periods of a few seconds with low concentrations of Mg-[(32)P]ATP, the reaction was stopped with trichloroacetic acid and determinations were made of the phosphate bound to the acid-washed, and in some cases solvent-extracted, residue. 2. At 20 mum-ATP, at 37 degrees and in the presence of Na(+) ions, 30-50 mumumoles of phosphate/mg. of microsomal protein were bound by the preparation within 1 sec. of starting the reaction; little further change in level occurred until hydrolysis of ATP exceeded 50%, when the bound phosphate began to decline fairly rapidly to the zero-time value. 3. At 20mum-ATP without Na(+) ions present or in the presence of K(+) ions, the level of bound phosphate increased gradually and did not decline as ATP hydrolysis approached completion. 4. Potassium ions either inhibited the formation of Na(+)-dependent bound phosphate or, when added during the course of the reaction, rapidly reduced its level. 5. At 200 mum-ATP the bound phosphate formed in the presence of Na(+) ions appeared to consist of a mixture of the unstable Na(+)-dependent type and the stable type requiring only Mg(2+) ions for its formation. 6. Non-radioactive ATP added during the course of the reaction at 20 mum-ATP with Na(+)ions present rapidly discharged virtually all the bound (32)P counts; at 200 mum-ATP only a proportion of the label was similarly discharged. The Na(+)-dependent bound phosphate is therefore turning over, in contrast with that formed in the absence of Na(+)ions, which proved more stable. 7. The Na(+)-dependent bound phosphate was not in the form of ATP; experiments with [(14)C]ATP instead of [(32)P]ATP showed a small and invariable binding of ATP by the preparation unaffected by Na(+) ions or time of incubation. 8. Under the usual conditions employed in this work ouabain stimulated formation of Na(+)-dependent bound phosphate when Na(+) ions were suboptimum and inhibited it when optimum Na(+) ions were present. 9. The Na(+)-dependent binding reaction under present conditions did not involve incorporation into phosphorylserine groups. 10. The relation of the findings to the (Na(+),K(+))-ATPase of the preparation, and to observations in brain slices appearing to implicate phosphorylserine groups in cation transport, is discussed.

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Enzyme transfer of phosphate from adenosine triphosphate to protein-bound serine residues in cerebral microsomes.

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