Effect of Vitamin K (Menadione) on Choline Esterase Activity,Acetylcholine Synthesis,and Striated Muscle. ∗

Summary

1. The effect of menadione in concentrations from 1×10⁻⁷ to 2.5×10⁻³ mol. on the synthesis of acetylcholine, on the activity of choline esterase, and on the effect of some chemical agents in inducing muscle contraction was investigated. 2. In the presence of menadione the synthesis of acetyl-choline is decreased. 3. The activity of choline esterase was not modified by concentrations of menadione up to 1×10⁻³ mol. and was decreased by higher concentrations (man-ometric method and striated muscle). 4. Menadione increased the effect of potassium in inducing muscle contraction. 5. In high concentrations (2.5×1(H mol.) it induced a contraction of the striated muscle. 6. The effect of methylene blue is similar to that of menadione except that methylene blue is a potent inhibitor of the choline esterase. 7. The mechanisms of the effects of menadione are discussed in relation to its ability to react with -SH groups, to its positive oxidation-reduction potential, and to its action on the aerobic glycolysis.