title: Stability and photochemical properties of vanadate-trapped nucleotide complexes of gizzard myosin in the 6S and 10S conformations: identification of an active-site serine.
abstract: The properties of divalent metal.ADP.vanadate (V(i)) complexes of the 6S extended and 10S folded conformations of gizzard myosin before and after UV irradiation have been studied. The half-lives of both 6S and 10S myosin.MgADP.V(i) complexes in the dark at 0 degrees C are on the order of 2 weeks. Brief irradiation with UV light, however, photomodified the enzyme as suggested by changes in the NH(4+)-, K(+)-, and Ca(2+)-ATPase activities, and destabilized the complexes. The 6S complex, when irradiated, released ADP and V(i) rapidly (t1/2 less than or equal to 1 min) as has been observed in comparable experiments with skeletal myosin subfragment 1 (S1) [Grammer et al. (1988) Biochemistry 27, 8408-8415]. The irradiated 10S complex released approximately 20% of the ADP and V(i) rapidly (t1/2 less than or equal to 1 min), but the remainder stayed trapped, possibly as the vanadyl (VO2+).ADP complex, for much longer times (t1/2 approximately 8 h). The site of photomodification was sought by reducing both photomodified 6S and 10S myosin with NaB3H4. Amino acid composition analyses identified [3H]serine as the only labeled residue(s), suggesting that the hydroxymethyl group of serine had been oxidized to an aldehyde as shown previously for photomodified skeletal myosin S1 [Cremo et al. (1989) J. Biol. Chem. 264, 6608-6611]. The 29-kDa NH2-terminal tryptic peptide from the heavy chain was found to contain essentially all of the [3H]serine. Preparations of 6S and 10S [3H]myosin were digested exhaustively with trypsin. An identical [3H]peptide was purified from each preparation and its sequence determined to be Glu169-Asp-Gln-Ser-Ile-Leu-(Cys)-Thr-Gly-[3H]Ser-Gly-Ala-Gly-Ly s183.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Biochemistry/Biophysics, Washington State University, Pullman 99164-4660.
authors.forename: D G
authors.initials: DG
authors.lastname: Cole
authors.forename: R G
authors.initials: RG
authors.lastname: Yount
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism / Q000494:pharmacology; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002645:Chickens; D005895:Gizzard, Avian; D007700:Kinetics; D008670:Metals; D008969:Molecular Sequence Data; D009130:Muscle, Smooth / Q000378:metabolism*; D009218:Myosins / Q000737:chemistry* / Q000378:metabolism*; D010446:Peptide Fragments / Q000302:isolation & purification; D010777:Photochemistry; D011485:Protein Binding; D011487:Protein Conformation; D012689:Sequence Homology, Nucleic Acid; D012694:Serine; D014316:Tritium; D014638:Vanadates / Q000494:pharmacology*
chemical_list: D008670:Metals; D010446:Peptide Fragments; D014316:Tritium; D014638:Vanadates; D012694:Serine; D000244:Adenosine Diphosphate; D000251:Adenosine Triphosphatases; D009218:Myosins