Identification of the endogenous substrates of rat liver cytosol “phosvitin kinase”

1. 1. Highly purified "phosvitin kinase" from rat liver cytosol has been found to be active on a low mol. wt peptide fraction and not on larger phosphoproteins isolated from the same source and resolved by Sepharose 6B gel chromatography. 2. 2. Such endogenous substrates of phosvitin kinase are resolved by 45% polyacrylamide gel electrophoresis into at least two components, both in the mol. wt range between 2000 and 3000. 3. 3. Cytosol phosphopeptides are devoid of the (ser-P)n blocks characteristic of typical acidic phosphoproteins like phosvitin and casein; nevertheless their affinity for the kinase is even greater than that displayed by te foreign substrate phosvitin. © 1976.