INACTIVATION AND REACTIVATION OF LIVER PHOSPHORYLASE IN VITRO: EFFECT OF GLUCOSE 1-PHOSPHATE

LUIZ A. FAGUNDES ¹ and RICHARD B. COHEN ¹

¹ Department of Pathology, Harvard Medical School, and The James Homer Wright Pathology Laboratories of the Massachusetts General Hospital, Boston, Massachusetts

In this study it has been demonstrated that preincubation of rat liver sections in a solution of PVP and buffer for ten min resulted in the inactivation of phosphorylase. Subsequent incubation in substrate solution containing ATP and Mg⁺⁺ in addition to the routine constitutes reactivated phosphorylase. Mg⁺⁺ was demonstrated as being essential to this ATP-mediated reactivation. AMP replacing ATP and Mg⁺⁺ in the substrate solution was capable of reactivation to a considerably lesser extent. In the recently fed animal preincubation inactivation with subsequent reactivation in substrate solution resulted in more diffuse and intense phosphorylase activity than could be demonstrated by simple incubation in the same substrate without prior incubation. The addition of G-1-P in varying concentrations to the preincubating solution prevented this subsequent increase in activity following substrate incubation. G-1-P in the preincubating solution did not exert this depressing effect when livers of starved animals were used. Sodium fluoride in the preincubation solution prevented inactivation of phosphorylase. It was suggested that G-1-P, glycogen or some intermediate product may form complexes with enzyme protein which tend to reduce its capacity to react with exogenous substrate.

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