The possible role of myosin A1 light chain in the weakening of actin-myosin interaction.
The effects resulting from the removal of the N-terminus of myosin A1 by limited papain cleavage are investigated. The myosin and heavy meromyosin K+-ATPase and Ca2+-ATPase activities, and actin-activated ATPase activity of heavy meromyosin (HMM) and subfragment-1, are studied. Myosin and HMM preparations devoid of the A1 N-terminus exhibits lower Ca2+-ATPase activities at low ionic strength whereas no differences in K+- or Ca2+-ATPase activities are observed at high ionic strength. Direct binding of actin to monomeric myosin under K+-activated ATPase conditions is much more effective for myosin containing a shortened A1 light chain. The kinetic constants K(app) for actin and V(max) are calculated from actin-activation curves for HMM and subfragment-1. The kinetic constants for HMM are determined under conditions assuring saturation of regulatory light chains (RLC) either with Mg2+ or Ca2+. The removal of the A1 N-terminus influences the actin-myosin interaction in a Ca2+- and phosphorylation-dependent manner; in most cases, this leads to an increase in affinity. In the case of subfragment-1, the removal of the N-terminus of A1 led to a decrease in affinity. It is reasonable to assume that the intact A1 light chain may cause weakening of the actin-myosin interaction under certain conditions. This weakening may be regulated by RLC phosphorylation and RLC-bound calcium-for-magnesium exchange. Such an effect requires a structural minimum that is present in HMM but not in subfragment-1. Implications of such a role for the A1 N-terminus in the myosin-actin interaction are discussed.
Stepkowski
D
D
Department of Muscle Biochemistry, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw. DAREKS@NENCKI.GOV.PL
Efimova
N
N
Paczyņska
A
A
Moczarska
A
A
Nieznańska
H
H
Kakol
I
I
D000199:Actins / Q000378:metabolism* / Q000494:pharmacology; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D027682:Cation Transport Proteins; D007700:Kinetics; D018994:Myosin Light Chains / Q000737:chemistry* / Q000502:physiology*; D015879:Myosin Subfragments / Q000378:metabolism; D009218:Myosins / Q000378:metabolism*; D009994:Osmolar Concentration; D010206:Papain / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism; D010766:Phosphorylation; D011817:Rabbits; D013329:Structure-Activity Relationship; D013438:Sulfhydryl Compounds / Q000378:metabolism
D000199:Actins; D027682:Cation Transport Proteins; D018994:Myosin Light Chains; D015879:Myosin Subfragments; D010446:Peptide Fragments; D013438:Sulfhydryl Compounds; D010206:Papain; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; C022761:potassium transporting ATPase; D009218:Myosins; D000252:Calcium-Transporting ATPases