Author:
Engers H. D.,Bridger W. A.,Madsen N. B.
Abstract
In order to confirm the kinetic mechanism which was proposed for rabbit muscle phosphorylase a on the basis of initial rate studies and UDP-glucose inhibition experiments, isotope exchange studies at equilibrium were performed, both in the presence and absence of the modifier AMP.Both the 14C-glucose [Formula: see text] and the [Formula: see text]1-phosphate equilibrium exchange rates increased to a maximum as the concentrations of the varied substrates became saturating, either in the presence or absence of AMP. The plateaus observed in these experiments indicate the lack of inhibition of the exchange of one pair of substrates when the concentration of the other substrate pair was raised, and confirms the proposed random addition of substrates to the enzyme.The fact that similar exchange rates were observed for either reaction direction reinforced the concept that rapid equilibrium conditions apply to the phosphorylase a mechanism; i.e. the interconversion of the ternary complexes tends to be the rate-limiting step in the reaction sequence.Maximal velocities determined from initial rate data reported in the previous paper agreed with those calculated from isotope exchange rates.
Publisher
Canadian Science Publishing
Cited by
22 articles.
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