title: A 72,000-mol-wt protein from tomato inhibits rabbit acto-S-1 ATPase activity.
abstract: Tomato activation inhibiting protein (AIP) is a molecule of an apparent molecular weight of 72,000 that co-purifies with tomato actin. In an assay system containing rabbit skeletal muscle F-actin and rabbit skeletal muscle myosin subfragment-1 (myosin S-1), tomato AIP dissociated the acto-S-1 complex in the absence of Mg+2ATP and inhibited the ability of F-actin to activate the low ionic strength Mg+2ATPase activity of myosin S-1. At a molar ratio of 5 actin to 1 AIP, a 50% inhibition of the actin-activated Mg+2ATPase activity of myosin S-1 was observed. The inhibition can be reversed by raising the calcium ion concentration to 1 X 10(-5) M. The AIP had no effect on the basal low ionic strength Mg+2ATPase activity of myosin S-1 in the absence of actin. The protein did not bind directly to actin nor did it cause depolymerization or aggregation of F-actin but appeared, instead, to interact with the actin binding site on myosin S-1. Since AIP is a potent, reversible inhibitor of the rabbit acto-S-1 ATPase activity, it is postulated that it may be responsible for the low levels of actin activation exhibited by tomato F-actin fractions containing the AIP.
mesh_terms: D000199:Actins / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors*; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase; D002118:Calcium / Q000378:metabolism; D008970:Molecular Weight; D015879:Myosin Subfragments; D009218:Myosins / Q000037:antagonists & inhibitors*; D010446:Peptide Fragments / Q000037:antagonists & inhibitors*; D010944:Plants / Q000032:analysis*; D011506:Proteins / Q000302:isolation & purification / Q000494:pharmacology*; D011817:Rabbits; D000097795:ATPase Inhibitory Protein
chemical_list: D000199:Actins; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; D002118:Calcium; D015879:Myosin Subfragments; D009218:Myosins; D010446:Peptide Fragments; D011506:Proteins; D000097795:ATPase Inhibitory Protein