Characterization of carbethoxylated actin.
The carbethoxylation of histidine residues in G-actin impairs actin polymerization. The histidine residue essential for polymerization was identified as histidine-40 [Hegyi, G., Premecz, G., Sain, B., & Mühlrad, A. (1974) Eur. J. Biochem. 44, 7-12]. Non-polymerizable actin was separated from the polymerizable fraction after partial carbethoxylation. The non-polymerizable actin recovered the ability to polymerize following addition of phalloidin. Taking into account the evidence that phalloidin does not bind to G-actin in the absence of salt, the results indicate that the actin monomer undergoes a conformational change and subsequently binds phalloidin before polymerization. The resulting polymers activated S1 ATPase activity as effectively as control F-actin. In the presence of tropomyosin and troponin, a strong inhibition of actin-activated ATPase activity was observed in the absence of Ca2+, although no inhibition was observed in the presence of Ca2+. These results indicate that His-40 is not directly involved in a myosin binding site nor in a tropomyosin-troponin binding site.
Miki
M
M
Department of Anatomy, University of Sydney, N.S.W., Australia.
D000199:Actins / Q000032:analysis*; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D010590:Phalloidine; D011108:Polymers; D011817:Rabbits
D000199:Actins; D011108:Polymers; D010590:Phalloidine; D017301:Ca(2+) Mg(2+)-ATPase