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The Sulfhydryl Groups of Rabbit Muscle Adenosine Triphosphate-Adenosine Monophosphate Phosphotransferase

ACTIVITY OF ENZYME TREATED WITH MERCURIALS

From the ¹ From the Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire

The reaction of rabbit muscle myokinase (adenosine triphosphate-adenosine monophosphate phosphotransferase, EC 2.7.4.3) with p-hydroxymercuribenzoate and p-mercuribenzenesulfonate in the presence of 0.5 m NaCl results in the stoichiometric blocking of both sulfhydryl groups on the enzyme molecule and the formation of myokinase-mercurial complexes possessing about 45% of their initial activity.

Kinetic studies show that the K_m of the myokinase-p-hydroxymercuribenzoate complex does not differ significantly from that of intact myokinase, indicating that the sulfhydryl groups are not involved in substrate binding.

Reaction of myokinase with structural analogues of p-hydroxymercuribenzoate results in the formation of myokinase-mercurial complexes that possess varying amounts of initial enzymatic activity. Inhibition increases with increasing size of the mercurial substituted.

The role which the sulfhydryl groups might have in processes other than substrate binding or enzyme catalysis is discussed, along with possible steric effects brought about by the mercurial substituents.

An improved method for the purification of myokinase is also described.

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