The Action of Ninhydrin on the Enzymatic and Actincombining Properties of Myosin

Abstract

SummaryNinhydrin at 5 I-tM per mg. myosin produces 90 per cent. inhibition of luyosin-ATP-ase at pH 9.0 in 3 hours at 5°C. At pH 7.0 the same inhibition is produced by 35 I-tM ninhydrin per mg. myosin. This inhibition is reversed by cysteine, the release being complete after one hour's treatment of the myosin by ninhydrin, but incomplete, except with very high cysteine concentrations, after three hours' treatment of the myosin. Other amino acids did not release the inhibition produced by ninhydrin.The addition of actin to myosin treated with ninhydrin at concentrations which produced over 90 per cent. inhibition of the ATP-ase resulted in a rise in viscosity similar to that encountered with untreated myosin. The addition of ATP to ninhydrin-treated actomyosin, however, usually caused a precipitation of the actomyosin rather than a dissociation into myosin and actin.The removal of -SH groups of the myosin by ninhydrin was demonstrated by the disappearance of the nitroprusside reaction, but attempts to titrate -SH quantitatively in the presence of ninhydrin were unsuccessful.

The adenosinetriphosphatase activity of myofibrils isolated from skeletal muscle

“…On the other hand, however, the effects of a variety of sulphydryl reagents (Bailey & Perry, 1947), incubation at 370 and exposure to acid (Perry, 1947), on the adenosinetriphosphatase and actomyosin-forming activities of myosin suggest that these properties are closely related. These latter results are not in complete accord with those of Gilmour & Calaby (1949), who used ninhydrin to oxidize the myosin sulphydryl groups. The only specific criterion of actomyosin formation is the decrease in viscosity obtained when adenosinetriphosphate is added to the complex.…”