Effects of proteolysis on the adenosinetriphosphatase activities of thymus myosin
Limited proteolysis was used to identify regions on the heavy chains of calf thymus myosin which may be involved in ATP and actin binding. Assignments of the various proteolytic fragments to different parts of the myosin heavy chain were based on solubility, gel filtration, electron microscopy, and binding of /sup 32/P-labeled regulatory light chains. Chymotrypsin rapidly cleaved within the head of thymus myosin to give a 70,000-dalton N-terminal fragment and a 140,000-dalton C-terminal fragment. These two fragments did not dissociate under nondenaturing conditions. Cleavage within the myosin tail to give heavy meromyosin occurred more slowly. Cleavage at the site 70,000 daltons from the N-terminus of the heavy chain caused about a 30-fold decrease in the actin concentration required to achieve half-maximal stimulation of the magnesium-adenosinetriphosphatase (Mg-ATPase) activity of unphosphorylated thymus myosin. The actin-activated ATPase activity of this digested myosin was only slightly affected by light chain phosphorylation. Actin inhibited the cleavage at this site by chymotrypsin. In the presence of ATP, chymotrypsin rapidly cleaved the thymus myosin heavy chain at an additional site about 4000 daltons from the N-terminus. Cleavage at this site caused a 2-fold increase in the ethylenediaminetetraacetic acid-ATPase activity and 3-fold decreases in the Ca/sup 2 +/- and Mg-ATPase activities of thymus myosin. Thus, cleavage at the N-terminus of thymus myosin was affected by ATP, and this cleavage altered ATPase activity. Papain cleaved the thymus myosin heavy chain about 94,000 daltons from the N-terminus to give subfragment 1. Although this subfragment 1 contained intact light chains, its actin-activated ATPase activity was not affected by light chain phosphorylation.
- Research Organization:
- National Institute of Health, Bethesda, MD
- OSTI ID:
- 5994831
- Journal Information:
- Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 26:15; ISSN BICHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
62 RADIOLOGY AND NUCLEAR MEDICINE
ACID ANHYDRASES
ACTIN
ALKALINE EARTH METAL COMPOUNDS
ATP-ASE
AUTORADIOGRAPHY
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BODY
CALCIUM COMPOUNDS
CATIONS
CHARGED PARTICLES
CHEMICAL REACTIONS
CHYMOTRYPSIN
CONFIGURATION INTERACTION
DAYS LIVING RADIOISOTOPES
DECOMPOSITION
ENZYMATIC HYDROLYSIS
ENZYME ACTIVITY
ENZYMES
GLOBULINS
HYDROLASES
HYDROLYSIS
IONS
ISOTOPES
LABELLED COMPOUNDS
LIGHT NUCLEI
LYMPHATIC SYSTEM
LYSIS
MAGNESIUM COMPOUNDS
MYOSIN
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
ORGANS
PEPTIDE HYDROLASES
PHOSPHOHYDROLASES
PHOSPHORUS 32
PHOSPHORUS ISOTOPES
PHOSPHORYLATION
PROTEINS
RADIOISOTOPES
SERINE PROTEINASES
SOLVOLYSIS
THYMUS