Protein kinase C delta accepts GTP for autophosphorylation

Protein kinase C delta (PKC delta) from porcine spleen exhibits a marked capacity for autophosphorylation. Autophosphorylation is much more efficient in the presence of GTP than of ATP (6-fold). 15 mol phosphate/mol enzyme is incorporated with GTP as phosphate donor. The activity of PKC delta for autophosphorylation with ATP is around 4 times that of the isoenzymes alpha, beta, gamma (cPKC), and with GTP it is around 24 times that of cPKC. The catalytic subunit of protein kinase A and the tyrosine kinase src are not or only slightly autophosphorylated in the presence of GTP. The autophosphorylation of PKC delta with GTP does not differ from that with ATP regarding its activation by TPA or bryostatin, its inhibition by staurosporine, the type of phosphorylated amino acids (serine and threonine) and the mode of reaction (intrapeptide reaction). However, different sites are phosphorylated with GTP and ATP, as indicated by the amount of phosphate incorporated and by phosphopeptide mapping.