STUDIES ON PROPERTIES OF CHEMICALLY MODIFIED ACTIN .3. CARBETHOXYLATION

Diethylpyrocarbonate was used for the specific carbethoxylation of the histidyl residues of G- and F-actins. The characteristic properties of carbethoxylated actins were studied. The extent of carbethoxylation depended on the actin to reagent ratio, and equal numbers of histidyl residues were carbethoxylated in G- and F-actins. The number of tyrosine and SH groups did not change on diethylpyrocarbonate treatment. 30% of the bound nucleotide of G-actin was removed, whereas a high degree of carbethoxylation did not change the bound nucleotide of F-actin. The characteristic properties of F-actin (viscosity, repolymerizability, actomyosin formation, activation of myosin ATPase) were not altered by the treatment even on carbethoxylation of 70% of the histidyl residues. The characteristic properties of G-actin (polymerizability, actomyosin formation and activation of myosin ATPase) were almost lost on carbethoxylation of about half the histidyl residues. The treatment did not change the helix content of G-actin (the 233-mμ Cotton effect). These results lead to the assumption that the histidyl residues, which have some role in determining the characteristic properties of actin, are buried in F-actin. © 1969.