Partial purification and characterization of a 60000‐dalton phosphoprotein from pig heart tissue

Abstract

A 60000‐dalton phosphoprotein (pp60) was purified up to 104‐fold by a combination of low‐ionic‐strength extraction, ammonium sulfate fractionation, on‐exchange and affinity chromatography, all in detergent‐free buffer. Fractionation on ω‐aminohexylagarose column shows that pp60 actually consists of two different polypeptides of similar molecular mass (pp60ω1 and pp60ω2). Partial hydrolysis with proteases of the proteins 32P‐labeled in vitro indicates that pp60ω1 and pp60ω2 are similar but not identical. On the other hand, individual phosphoamino acid analysis reveals that pp60ω1 is phosphorylated primarily at serine residues while pp60ω1 is phosphorylated almost equally at serine and threonine residues. Partial hydrolysis with proteases has been also used to explore a possible relationship between the pp60's and the transforming protein of Rous sarcoma virus (pp60v‐src). Our data suggest that pp60v‐src also consists of two different polypeptides chemically homologous to the presently purified pp60's. Copyright © 1984, Wiley Blackwell. All rights reserved