Glucagon-induced phosphorylation of pyruvate kinase (type L) in rat liver slices

• The effect of glucagon on the phosphorylation of pyruvate kinase in 32P-labelled slices from rat liver was investigated. Pyruvate kinase was isolated by immunoadsorbent chromatography. The enzyme was partially phosphorylated in the absence of added hormone (0.2 mol of phosphate/mol of enzyme subunit). Upon incubation with 10−7 M glucagon, the incorporation of [32P]phosphate was 0.6–0.7 mol/mol of enzyme subunit. Concomitantly, the concentration of intracellular cyclic 3′,5′-AMP increased from 0.3 to 3.2 μM. The phosphorylation inhibited the enzyme activity at low concentrations of phosphoenolpyruvate (60% at 0.5 mM). Almost maximal phosphorylation of the enzyme was reached within 2 min after the addition of glucagon. The concentration of hormone giving half maximal effect on the pyruvate kinase phosphorylation was about 7×10−9M. The inactivation of the enzyme paralleled the increase in phosphorylation. It is concluded that pyruvate kinase is phosphorylated in the intact liver cell.

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MEDICIN OCH HÄLSOVETENSKAP  -- Medicinska och farmaceutiska grundvetenskaper -- Andra medicinska och farmaceutiska grundvetenskaper (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Basic Medicine -- Other Basic Medicine (hsv//eng)

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