Identification of a new 80 k isoform of phosphatidylinositol 4‐phosphate 5‐kinase from bovine brain

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Abstract
Phosphatidylinositol 4‐phosphate 5‐kinase is associated with bovine brain microsomes to an extent of approximately 65% of the total cellular enzyme activity. This membrane‐associated kinase activity can be solubilized with Triton X‐114. Following polyacrylamide gel electrophoresis in the presence of SDS the enzyme can be renaturated from gel slices in the presence of desoxycholate and Triton X‐100. Catalytic activity appears at an apparent molecular weight of 80 k. Analysis of the reaction product formed by the 80 k protein reveals the existence of a 5‐phosphotransferase, identifying the 80 k polypeptide as a new phosphatidylinositol 4‐phosphate 5‐kinase isoform.