title: The effect of nucleotide upon a specific isomerization of actomyosin subfragment 1.
abstract: The binding of actin to myosin subfragment 1 (S1) has been shown to occur as a two-step reaction [Coates, Criddle & Geeves (1985) Biochem. J. 232, 351-356]. In the first step actin is weakly bound and the second step involves the complex isomerizing to a more tightly bound state. This isomerization can be followed specifically by monitoring the fluorescence of actin that has been covalently labelled with N-(pyren-1-yl)-iodoacetamide at Cys-374 [Geeves, Jeffries & Millar (1986) Biochemistry 25, 8454-8458]. We report here that the presence of nucleotides and nucleotide analogues affects the equilibrium between the strongly bound and weakly bound states (referred to as K2). In the presence of ATP, [gamma-thio]ATP or ADP and vanadate a value of approx. less than 10(-2) was estimated for K2. In the presence of PPi or ADP a value of approx. 2.3 or 10 respectively was obtained. An increase in KCl concentration or the presence of 40% ethylene glycol was found to decrease K2 in the presence of ADP. The data presented here are consistent with the two-step binding model proposed by Geeves, Goody & Gutfreund [(1984) J. Muscle Res. Cell Motil. 5, 351-361], where it was suggested that the transition between weakly bound and strongly bound states is closely associated with the force-generating event in whole muscle.
authors.affiliation: Department of Biochemistry, School of Medical Sciences, University of Bristol, U.K.
authors.forename: M A
authors.initials: MA
authors.lastname: Geeves
authors.forename: T E
authors.initials: TE
authors.lastname: Jeffries
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D019855:Ethylene Glycol; D005026:Ethylene Glycols / Q000494:pharmacology; D007536:Isomerism; D008027:Light; D015879:Myosin Subfragments; D009218:Myosins / Q000378:metabolism*; D009711:Nucleotides / Q000494:pharmacology*; D010446:Peptide Fragments / Q000378:metabolism*; D010710:Phosphates / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D012542:Scattering, Radiation; D013050:Spectrometry, Fluorescence; D014638:Vanadates
chemical_list: D005026:Ethylene Glycols; D015879:Myosin Subfragments; D009711:Nucleotides; D010446:Peptide Fragments; D010710:Phosphates; C022571:adenosine 5'-O-(3-thiotriphosphate); D014638:Vanadates; D000244:Adenosine Diphosphate; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D009218:Myosins; D019855:Ethylene Glycol