A rabbit skeletal muscle glycogen synthase kinase, designated PC0.7 (A. A. DePaoli-Roach, Z. Ahmad, and P. J. Roach, 1981, J. Biol. Chem. 256, 8955-8962), has been shown to belong to that class of casein and phosvitin kinases inhibited by heparin. The heparin concentration required for half-maximal inhibition (I0.5) was in the range 0.04-0.15 μg/ml when glycogen synthase, phosvitin, or β-casein A were substrates for phosphorylation. Heparin also inhibited (I0.5 = 0.05 μg/ml) the previously observed autophosphorylation of the β-subunit (Mr 25,000) of the protein kinase. The enzyme was also affected by the polyamines spermine and spermidine, but less so by putrescine. With glycogen synthase or β-casein A as substrates, spermine and spermidine stimulated PC0.7 activity although the extent depended on Mg2+ concentration. With phosvitin as substrate, spermine and spermidine activated at low Mg2+ levels but spermine inhibited at higher Mg2+ concentrations. KCl at 0.05 to 0.15 m considerably alleviated heparin inhibition, and also tended to reverse spermine effects on measured activity. Histone and spermine suppressed the inhibition by heparin. Heparin and polyamine effects on PC0.7 are thus interdependent and also modified by various factors including ionic strength, Mg2+, and histone. Careful consideration must be given to such interactions in assessing any possible physiological relevance of effectors such as heparin or polyamines.
ASJC Scopus subject areas
- Molecular Biology