Studies on heart phosphofructokinase. Nature of the enzyme desensitized to allosteric control by photo-oxidation and by acylation with ethoxyformic anhydride.

摘要: Abstract Phosphofructokinase from sheep heart was desensitized to ATP inhibition by photo-oxidation of the enzyme in presence methylene blue. Amino acid analyses were performed on native and photo-oxidized enzyme. The results showed that a total 18.2 moles histidine per 105 g an average 3 lost after photo-oxidation. number cysteine residues reduced 14.0 6.6 moles/105 following such treatment. No other amino affected with possible exception methionine. allosteric kinetics phosphofructokinase studied treatment ethoxyformic anhydride at pH 6.1. Evidence reagent reacted came spectrophotometric studies fact reaction could be reversed hydroxylamine neutral pH. Spectrophotometric determination product reaction, N-ethoxyformyl histidine, agreed well 14C-ethoxyformyl groups formed protein range 0 4 At 8.2, containing 3.5 ethoxyformylated indistinguishable except for 22 44% decrease Vmax. However, 6.9, same derivative characterized (a) loss sensitivity ATP, (b) cooperativity fructose-6-P, (c) citrate activation AMP or 3',5'-cyclic AMP. degree these regulatory properties dependent extent modification Maximum desensitization occurred when protein. Brief resulted basis catalytic activity inhibition. Ethoxyformylation normally carried out fructose-1,6-di-P. effects incubation absence compounds. Incubation mild similar observed behavior sucrose gradients identical fructose-6-P. substrates, somewhat more aggregated than are compared those It is probable alteration both cases largely responsible