Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.6.3.1 (Mg2+-ATPase)
 1,484 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The steady-state kinetics of the K+, Ca2+, and Mg2+-activated adenosine triphosphatase (ATPase) activities of rabbit skeletal myosin were investigated in the substrate concentration range from 0.05 microM to 5 mM and found not to follow Michaelis-Menten kinetics but rather to display biphasic behavior. The Ca2+-ATPase activity of myosin chymotryptic subfragment-1 (S-1), which has only one active site, also exhibits biphasic kinetics, thus excluding the possibility that the biphasic behavior is caused by negative cooperativity between the two active sites of myosin. Myosin K+ and Mg2+-ATPase are both activated by 5'-adenyl methylenediphosphonate (AdoPP[CH2]P) in a competitive manner at high substrate concentrations; i.e. the maximal velocity observed at high substrate concentrations is independent of the AdoPP[CH2]P concentration. This result provides evidence for substrate activation via binding to a regulatory site. Pyrophosphate inhibits myosin ATPase in a competitive manner at low substrate concentrations and in an uncompetitive manner at high substrate concentrations, with the uncompetitive Ki being smaller than the competitive Ki; i.e. pyrophosphate binds more tightly to the effector site than to the active site.
 ...
PMID:Biphasic steady-state kinetics of myosin adenosine triphosphatase. Evidence for a substrate effector site. 610 32

Enzymatic and structural studies of human cardiac myosin from young and old subjects have been investigated to determine possible changes in myosin properties in aging hearts. Human ventricular myosin from old subjects (47-70 years old) has lower actin-activated ATPase activity than and increased alkaline sensitivity as compared to myosin from young subjects (1-132 months old). Ca2+-and K+(EDTA)-ATPase activities, pyrophosphate gel patterns and one-dimensional peptide mapping of heavy chains of ventricular myosin from old subjects are similar to those observed for myosin from young subjects. Atrial myosin from human hearts differs significantly from ventricular myosin in that the Ca2+-, Mg2+- and actin-activated myosin Mg2+-ATPase activities of atrial myosin are significantly higher than those of ventricular myosin. Pyrophosphate gel electrophoresis patterns and peptide mapping of heavy chains of atrial myosin are also different from those of ventricular myosin. Unlike ventricular myosin, atrial myosin from young hearts is similar to that of atrial myosin from old hearts in its enzymatic and structural properties.
 ...
PMID:Effects of aging on atrial and ventricular human myosin. 622 46