Structural aspects of skeletal muscle F-actin as studied by tryptic digestion: evidence for a second nucleotide interacting site.
Trypsin was used as a probe of F-actin conformation. F-actin is known to be refractory to proteolysis [Jacobson, G.R. and Rosenbusch, J.P. (1976) Proc. Natl. Acad. Sci. U.S. 73, 2742-2746]. However, here it was found that F-actin could also be digested by trypsin to a 33-kDa fragment (like G-actin) when free MgADP is present in the medium. The amounts of degradation of F-actin depended on the ADP concentration; saturation occurred at about 0.5 mM. Elimination of divalent cations from the medium completely suppressed the effect of ADP on the digestion of F-actin. Other nucleotides were also examined. The effect decreased in the order ADP greater than ATP much greater than IDP greater than GDP = UDP. Adenine, adenosine, AMP, and PPi had no effect at all. epsilon-ADP had the effect, and its fluorescence was changed on the addition of F-actin. The intrinsic tryptophan fluorescence spectrum of F-actin was ADP-dependent. These results suggest the presence of a second nucleotide interacting site on actin and that ADP interaction at this site induces conformational changes in monomeric actin molecule in F-actin filaments.
Hozumi
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Department of Physiology, Nagoya City University Medical School, Aichi.
D000199:Actins; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002918:Chymotrypsin / Q000378:metabolism; D009391:Nephelometry and Turbidimetry; D009711:Nucleotides / Q000378:metabolism*; D011487:Protein Conformation; D011817:Rabbits; D013050:Spectrometry, Fluorescence; D014357:Trypsin / Q000378:metabolism*
D000199:Actins; D009711:Nucleotides; D000244:Adenosine Diphosphate; D002918:Chymotrypsin; D014357:Trypsin; D017301:Ca(2+) Mg(2+)-ATPase