PROPERTIES AND ACTIVATION OF PHOSPHORYLASE-KINASE FROM SILKMOTH FAT-BODY

Phosphorylase kinase from pupal fat body of the silkmoth, Hyalophora cecropia, has been characterized with rabbit muscle phosphorylase b as substrate. The enzyme is converted from a non-activated to an activated form by incubation with ATP, Mg2+ and Ca2+ in an apparently autocatalytic process which was not stimulated by addition of cyclic AMP. It was not activated by inorganic phosphate (as reported by blowfly flight muscle phosphorylase kinase). The activated enzyme showed greater activity at pH 6.8, relative to that at pH 8.2, than the non-activated enzyme. Activity was stimulated by Ca2+, half-maximally at about 10-6 M and maximally at 10-4 M, but partial activity persisted with EGTA and no added Ca2+. The Arrhenius plot for the effect of temperature on activity was linear indicating an activation energy of 11,000 cal/mole. The Km for phosphorylase b was about 1 mg/ml both at 0°C and at 30°C. Activation of phosphorylase kinase may underlie the activation of fat body phosphorylase by shock stimuli, but the data do not explain the mechanism of phosphorylase activation induced by cold. Fat body of tobacco hornworm adults (Manduca sexta) exhibits phosphorylase phosphatase activity, catalyzing the conversion of rabbit muscle phosphorylase a to phosphorylase b. © 1979.