Phosphorylation of human red cell and liver pyruvate kinase. Differences between liver and erythrocyte L-type subunits.

Purified PK from human erythrocyte was phosphorylated by cAMP-dependent protein kinase type I from human erythrocyte membrane; this phosphorylation affected only the 'heavy L' subunit but not the L subunit. On the other hand, the L subunit of liver PK was highly phosphorylated. Thus it appears that the L subunits from erythrocyte and liver PK are not identical protein molecules.