Regulation of actomyosin ATPase activity by troponin-tropomyosin: effect of the binding of the myosin subfragment 1 (S-1) ATP complex

Journal Article · Fri May 01 00:00:00 EDT 1987 · Proc. Natl. Acad. Sci. U.S.A.; (United States)

DOI:https://doi.org/10.1073/pnas.84.10.3102· OSTI ID:5562120

Greene, L E; Williams, Jr, D L; Eisenberg, E

In the authors' model of regulation, the observed lack of cooperativity in the binding of myosin subfragment 1 (S-1) with bound ATP to the troponin-tropomyosin-actin complex (regulated actin) is explained by S-1 ATP having about the same affinity for the conformation of the regulated actin that activates the myosin ATPase activity (turned-on form) and the conformation that does not activate the myosin ATPase activity (turned-off form). This predicts that, in the absence of Ca/sup 2 +/, S-1 ATP should not turn on the regulated actin filament. In the present study, they tested this prediction by using either unmodified S-1 or S-1 chemically modified with N,N'-p-phenylenedimaleimide (pPDM S-1) so that functionally it acts like S-1 ATP, although it does not hydrolyze ATP. (/sup 14/C)pPDM and (/sup 32/P)ATP were used as tracers. They found that, in the absence of Ca/sup 2 +/, neither S-1 ATP nor pPDM S-1 ATP significantly turns on the ATPase activity of the regulated complex of actin and S-1 (acto S-1). In contrast, in the presence of Ca/sup 2 +/, pPDM S-1 ATP binding almost completely turns on the regulated acto S-1 ATPase activity. These results can be explained by their original cooperativity model, with pPDM S-1 ATP binding only approx. = 2 fold more strongly to the turned-on form that to the turned-off form of regulated actin. However, the results are not consistent with our alternative model, which predicts that if pPDM S-1 ATP binds to actin in the absence of Ca/sup 2 +/ but does not turn on the ATPase activity, then it should also turn on the ATPase activity in the presence of Ca/sup 2 +/.

• Research Organization: National Institutes of Health (NIH), Bethesda, MD (United States)
• OSTI ID: 5562120
• Journal Information: Proc. Natl. Acad. Sci. U.S.A.; (United States), Vol. 84:10
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
ATP-ASE
BIOCHEMICAL REACTION KINETICS
LABELLED COMPOUNDS
TRACER TECHNIQUES
MUSCLES
BIOCHEMISTRY
ACTIN
CARBON 14 COMPOUNDS
ENZYME ACTIVITY
MYOSIN
PHOSPHORUS 32
ACID ANHYDRASES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CHEMISTRY
DAYS LIVING RADIOISOTOPES
ENZYMES
GLOBULINS
HYDROLASES
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LIGHT NUCLEI
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
PHOSPHOHYDROLASES
PHOSPHORUS ISOTOPES
PROTEINS
RADIOISOTOPES
REACTION KINETICS
550201* - Biochemistry- Tracer Techniques