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

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Abstract
Microsomes from guinea-pig brain grey matter were incubated with [32P]ATP at 3 mM concentration and the phosphate bound to the acid-washed, lipid-free residue was determined. The binding process was Mg2+-dependent and resulted in the transfer of about 1-2 m[mu]moles of phosphate/mg. of protein/min. Under the conditions used univalent cations (Na+, K+ and Li+) inhibited the binding. 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. The bound phosphate formed with 3 m[image]-MgATP was stable; addition of Na+ or K+ ions to the already labelled preparation had no effect on the bound phosphate level. Bound phosphate was also formed when a solubilized fraction of the microsomes was incubated with ATP; univalent cations also inhibited this process. p-Chloromercuribenzoate reduced the binding by about 25%; the inhibition was restored by cysteine.