Effect of actin, ATP, phosphates, and pH on vanadate-induced photocleavage of myosin subfragment 1.
Near-UV irradiation in the presence of vanadate cleaves the heavy chain of myosin subfragment 1 at three specific sites located at 23, 31, and 74 kDa from the N-terminus. Increasing the pH from 6.0 to 8.5, gradually, reduces the efficiency of the cleavage and completely eliminates the 31-kDa cut. Actin specifically inhibits the photocleavage at the sites located 31 and 74 kDa from the N-terminus. ATP strongly protects from cleavage at the 23- and 31-kDa sites and less strongly from the cut at the 74-kDa site. ADP and pyrophosphate have similar, but less pronounced, effects as ATP. Orthophosphate inhibits the photocleavage at the 23- and 74-kDa sites with a similar efficiency. In the ternary actin-S-1-ATP complex, the photocleavage is inhibited at all sites, and the effects of actin and ATP are additive. Photocleavages affect the K+(EDTA)-, Ca2(+)-, and actin-activated ATPase activity of subfragment 1. Loss of all three ATPases is caused by cleavage at the 23-kDa site, while the cut at the 74-kDa site only leads to the loss of actin-activated ATPase activity. It is concluded that subfragment 1 contains at least two distinct phosphate binding sites, the first being part of the "consensus" ATP binding site wherein the 23-kDa photocleavage site is located. This site is responsible for the binding and hydrolysis of ATP. It is possible that the 31-kDa cleavage site is also associated with the "consensus" site through a loop. The 74-kDa cleavage site is a part of another phosphate binding site which may play a role in the regulation of the myosin-actin interaction.
Muhlrad
A
A
Department of Oral Biology, Hebrew University-Hadassah School of Dental Medicine, Jerusalem, Israel.
Peyser
Y M
YM
Ringel
I
I
D000199:Actins / Q000494:pharmacology*; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D015879:Myosin Subfragments / Q000378:metabolism*; D009218:Myosins / Q000378:metabolism; D010710:Phosphates / Q000494:pharmacology*; D010782:Photolysis; D011487:Protein Conformation; D011817:Rabbits; D014466:Ultraviolet Rays; D014638:Vanadates / Q000494:pharmacology*
D000199:Actins; D015879:Myosin Subfragments; D010710:Phosphates; D014638:Vanadates; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D009218:Myosins