title: Effects of tryptic digestion on myosin subfragment 1 and its actin-activated adenosinetriphosphatase.
abstract: Myosin subfragment 1 (S-1) was fluorescently labeled at its rapidly reacting thiol ("SH1"). Short exposure to trypsin cuts the S-1 heavy chain into three still-associated fragments (20K, 50K, and 27K) [Balint, M., Wolf, L., Tarcsafalvi, A., Gergely, J., & Sreter, F.A. (1978) Arch. Biochem. Biophys. 190, 793-799] which bind F-actin to the same extent as does the uncut labeled S-1, as indicated by time-resolved fluorescence anisotropy decay (at 4 degrees C, pH 7, in 0.15 M KC1 and 5 mM MgC12, +/- 1 mM ADP). These results are thus in agreement with turbidity measurements on similar systems as reported by Mornet et al. [Mornet, D., Pantel, P., Audemard, E., & Kassab, R. (1979) Biochem. Biophys. Res. Commun. 89, 925-932]. The excited-state lifetime of the fluorescent label on cut S-1 is indistinguishable from that on normal S-1 (+/- ADP, +/- F-actin). F-Actin activation of MgATPase of cut S-1 is lower than that for normal S-1 at moderate concentrations of F-actin, as reported by Mornet et al. (1979). But as the F-actin concentration is increased, the MgATPase activities for cut S-1 approach those for uncut S-1. In terms of an eight-species steady-state kinetics scheme involving actin binding to free S-1, S-1 . ATP, S-1. ADP X P, and S-1 . ADP, actin affinity for the species S-1 . ADP X P was found to be 13.4 times greater for uncut S-1 than for cut S-1 [at 24 degrees C, pH 7.0, in 3 mM KC1, 1 mM ATP, 1 mM MgCl2, and 20 mM N-[tris(hydroxymethyl)methyl]-2-aminoethanesulfonic acid].
mesh_terms: D000199:Actins / Q000494:pharmacology*; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D005454:Fluorescence Polarization; D008433:Mathematics; D015879:Myosin Subfragments; D009218:Myosins / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism*; D011817:Rabbits; D014357:Trypsin / Q000378:metabolism*
chemical_list: D000199:Actins; D015879:Myosin Subfragments; D010446:Peptide Fragments; D014357:Trypsin; D000251:Adenosine Triphosphatases; D009218:Myosins