title: A new, smaller actin-activatable myosin subfragment 1 which lacks the 20-kDa, SH1 and SH2 peptide.
abstract: The actin-dependent ATPase activity of myosin is retained in the separated heads (S1) which contain the NH2-terminal 95-kDa heavy chain fragment and one or two light chains. The S1 heavy chain can be degraded further by limited trypsin treatment into characteristic 25-, 50-, and 20-kDa peptides, in this order from the NH2-terminal end. The 20-kDa peptide contains an actin-binding site and SH1 and SH2, two thiols whose modification dramatically affects ATPase activity. By treating myosin filaments with trypsin at 4 degrees C in the presence of 2 mM MgCl2, we have now obtained preferential cleavage at the 50-20-kDa heavy chain site without any cleavage at the head-rod junction and hinge region in the rod. Incubation of these trypsinized filaments at 37 degrees C in the presence of MgATP released a new S1 fraction which lacked the COOH-terminal 20-kDa heavy chain peptide region. This fraction, termed S1'(75K), has more than 50% of the actin-activated Mg2+-ATPase activity of S1 and the characteristic Ca2+-ATPase and K+-EDTA ATPase activities of myosin. These results show that SH1 and SH2 are not essential for ATPase activity and that binding of actin to the 20-kDa region is not essential for the enhancement of the Mg2+-ATPase activity.
mesh_terms: D000199:Actins / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D008970:Molecular Weight; D009132:Muscles / Q000378:metabolism; D015879:Myosin Subfragments; D009218:Myosins / Q000302:isolation & purification / Q000378:metabolism*; D010446:Peptide Fragments / Q000032:analysis / Q000302:isolation & purification / Q000378:metabolism*; D011817:Rabbits; D014357:Trypsin
chemical_list: D000199:Actins; D015879:Myosin Subfragments; D010446:Peptide Fragments; D014357:Trypsin; D000251:Adenosine Triphosphatases; D009218:Myosins