RESUMO
Transient kinetic data of the hydrolysis of several nucleotides (TTP, CTP, UTP, GTP) by cardiac myosin subfragment 1 (S1) were analyzed to obtain values for the equilibrium constant for nucleotide binding and rate constants for the S1-nucleotide isomerization and the subsequent nucleotide hydrolysis as well as the magnitudes of the relative fluorescence enhancements of the myosin that occur upon isomerization and hydrolysis. These data are compared with data from a previous study with ATP. Nucleotide binding is found to be relatively insensitive to nucleotide ring structure, being affected most by the group at position C6. Isomerization and hydrolysis are more sensitive to nucleotide structure, being inhibited by the presence of a bulky group at position C2. Kinetic parameters decrease as follows: for binding, GTP greater than UTP approximately TTP greater than ATP greater than CTP; for isomerization, ATP greater than UTP approximately TTP approximately CTP greater than GTP; for hydrolysis, ATP greater than TTP greater than CTP approximately UTP greater than GTP. Fluorescence enhancements appear to be most dependent upon the relative values of the individual rate constants.
