title: The influence of substoichiometric concentrations of myosin subfragment 1 on the state of aggregation of actin under depolymerizing conditions.
abstract: In 3 mM KCl, 2 mM Tris/HCl pH 7.5, 22 degrees C, 0.38 microM myosin subfragment 1 delays the depolymerization of F-actin (7.2 microM measured as monomer). The depolymerization proceeds rapidly for a few minutes and then slows down suddenly when the ratio between the monomers in the actin filaments and myosin subfragment 1 reaches the value of 11. At this time myosin subfragment 1 is substantially all bound to the actin polymers which form an irregular and discontinuous network of filaments running in doublets and in triplets, perhaps cross-linked by myosin subfragment 1. Depolymerization proceeds then for several hours, apparently ending up with the formation of the 1:1 actin-S1 heteropolymer. The ratio between the monomers in the actin filaments and myosin subfragment 1 at the end of the rapid depolymerization process is different for different protein preparations and may be as low as 5.5. In 2 mM Tris/HCl pH 7.5, 25 degrees C, 1 microM myosin subfragment 1 is able to induce the formation of undecorated actin filaments from 12 microM ATP--G-actin. These filaments probably originate by redistribution of myosin subfragment 1 between the newly formed 1/1 actin-S1 heteropolymer and G-actin in the medium, a process which allows the transient formation of undecorated actin filaments.
authors.affiliation: Istituto di Chimica Biologica, Università di Ferrara, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Grazi
authors.forename: E
authors.initials: E
authors.lastname: Magri
authors.forename: L
authors.initials: L
authors.lastname: Rizzieri
mesh_terms: D051339:Actin Depolymerizing Factors; D000199:Actins / Q000378:metabolism*; D000255:Adenosine Triphosphate; D000818:Animals; D001665:Binding Sites; D011232:Chemical Precipitation; D051345:Destrin; D004591:Electrophoresis, Polyacrylamide Gel; D008840:Microfilament Proteins / Q000378:metabolism; D008854:Microscopy, Electron / Q000379:methods; D015879:Myosin Subfragments; D009218:Myosins / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism*; D011108:Polymers / Q000378:metabolism*; D011487:Protein Conformation
chemical_list: D051339:Actin Depolymerizing Factors; D000199:Actins; D051345:Destrin; D008840:Microfilament Proteins; D015879:Myosin Subfragments; D010446:Peptide Fragments; D011108:Polymers; D000255:Adenosine Triphosphate; D009218:Myosins