Studies on the properties of chemically modified actin. II. Trinitrophenylation

1. 4-10 amino groups of the 31 ε-amino groups of actin were trinitrophenylated by trinitrobenzene sulfonate, depending on the conditions of the reaction, and the characteristic properties of the trinitrophenylated actin were studied. 2. The effect of trinitrophenylation was more definite on the polymerizability of G-actin than on the depolymerization of the F-form. 3. The degree of actomyosin formation depended mainly on the pH of the trinitrobenzene sulfonate treatment. 4. The superprecipitation of synthetic actomyosin reconstituted from trinitrophenylated actin decreased more sharply when the actin was in the G-form than when it was in the F-form. 5. The myosin ATPase (ATP phosphohydrolase, EC 3.6.1.3) activation property of actin sharply decreased at a very low degree of trinitrophenylation in the presence of α-actinin. α-Actinin enhanced the ATPase activity of actomyosin reconstituted from control actin, but had no effect on the ATPase of actomyosins reconstituted from trinitrophenylated actins. 6. The ATPase activation by actin increased with the increasing degree of trinitrophenylation, when more than 1 mole amino groups per mole actin was trinitrophenylated.