title: Myosin subfragment 1 activates ATP hydrolysis on Mg(2+)-G-actin.
abstract: The interaction of myosin subfragment 1 isoenzyme A2 (S1A2) with Mg(2+)-G-actin was studied. Polarization titrations of 1,5-IAEDANS-Mg(2+)-G-actin and of epsilon ATP-Mg(2+)-G-actin with S1A2 provided evidence that, similar to Ca(2+)-G-actin, the proteins form a tight binary complex. Significant amounts of oligomeric forms of actin in the presence and absence of S1 were not detected. The effect of S1A2 on the rates of nucleotide and metal dissociation and hydrolysis from Mg(2+)-actin was measured. The hydrolysis rate for [gamma-32P]ATP-actin in the G-acto-S1A2 complex (k- = 0.016 s-1) was faster than the rate of 32P liberation from the complex (k- = 0.004 s-1), obtained by measuring the liberation of [32P]orthophosphate from [alpha-32P]ATP-actin in the presence of a large excess of alkaline phosphatase. This indicates that most of actin's ATP was hydrolyzed before it was released to solution and that the dissociating nucleotide was ADP, for which the dissociation rate is higher than that for ATP. In agreement with this mechanism, S1A2 accelerated the dissociation of epsilon ATP but inhibited the dissociation of epsilon ADP from the complex. The activation of actin's ATPase is specific for Mg(2+)-G-actin and does not occur in Ca(2+)-G-actin. The effect of deoxyribonuclease I on the rates of nucleotide dissociation and hydrolysis was examined.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Centre de Recherches de Biochimie Macromoléculaire, CNRS-INSERM U. 249, Université de Montpellier I, France.
authors.forename: A A
authors.initials: AA
authors.lastname: Kasprzak
mesh_terms: D000199:Actins / Q000378:metabolism*; D000244:Adenosine Diphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D003850:Deoxyribonuclease I / Q000494:pharmacology; D004355:Drug Stability; D004985:Ethenoadenosine Triphosphate / Q000378:metabolism; D005454:Fluorescence Polarization; D005456:Fluorescent Dyes; D006868:Hydrolysis; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D015879:Myosin Subfragments / Q000378:metabolism / Q000494:pharmacology*; D009218:Myosins / Q000378:metabolism; D009282:Naphthalenesulfonates; D010710:Phosphates / Q000378:metabolism; D011817:Rabbits
chemical_list: D000199:Actins; D004985:Ethenoadenosine Triphosphate; D005456:Fluorescent Dyes; D007527:Isoenzymes; D015879:Myosin Subfragments; D009282:Naphthalenesulfonates; D010710:Phosphates; C015195:1,N(6)-ethenoadenosine diphosphate; D000244:Adenosine Diphosphate; C006421:1,5-I-AEDANS; D000255:Adenosine Triphosphate; D003850:Deoxyribonuclease I; D000469:Alkaline Phosphatase; D009218:Myosins; D008274:Magnesium; D002118:Calcium