Studies on the amino groups of myosin ATPase. I. Effect of ethyl formyl hydroxamate on the ATPase activity of myosin

When myosin is treated by ethylformylhydroxamate (EFH), 3 to 8 carbethoxy groups are incorporated and a partial loss of free SH groups occurs. The Mg²⁺ and Ca²⁺ mediated ATPase activities of myosin increase, while the K⁺ activated activity decreases as the consequence of the treatment. If the SH groups of myosin are blocked by cystamine before the EFH treatment in order to prevent the reaction of SH groups with EFH, only NH₂ groups are carboxyethylated and the SH groups are fully recovered after treatment with thioglycollate. The ATPase activity of this myosin also differs from that of the original myosin: it increases in the presence of Mg²⁺ and decreases in the presence of Ca²⁺ or K⁺. This type of change is characteristic for myosin in which NH₂ groups have been modified. The reaction of 2,4,6 trinitrobenzene sulfonate (TBS) with myosin having either free or blocked SH groups has been studied. It was found that the NH₂ groups of SH blocked myosin reacted with TBS at the same rate as those of native myosin.