title: Cooperative effects in the peptidyltransferase center of Escherichia coli ribosomes.
abstract: We have measured the binding isotherms of C--A--C--C--A(3'NH)-[14C]Phe to the 70S ribosomes and 50S subunits of Escherichia coli and proposed a theoretical model for adsorption when cooperative interaction occurs between ligands that are adsorbed on ribosomes. Analysis of the experimental binding isotherms leads to the following conclusions. A ribosome (or subunit) binds two C--A--C--C--A(3'NH)-Phe molecules. The binding of C--A--C--C--A(3'NH)-Phe to a ribosome (or subunit) is a cooperative process, characterized by a cooperativity coefficient tau = 40 +/- 5 or more. The binding of C--A--C--C--A(3'NH)-AcPhe at the donor site of the peptidyltransferase center (association binding constant 1.5 X 10(6) M-1) and the binding of puromycin at the acceptor site also occur cooperatively with a coefficient of 10-25, the association binding constant of puromycin at the acceptor site being (1-2) X 10(4) M-1. The puromycin association binding constant at the donor site multiplied by the cooperativity coefficient of two interacting puromycin molecules absorbed on a ribosome equals 100-200 M-1.
mesh_terms: D000217:Acyltransferases / Q000378:metabolism*; D000495:Allosteric Site; D001426:Bacterial Proteins / Q000378:metabolism; D001667:Binding, Competitive; D004926:Escherichia coli / Q000201:enzymology*; D008034:Lincomycin / Q000494:pharmacology; D008956:Models, Chemical; D010458:Peptidyl Transferases / Q000378:metabolism*; D011691:Puromycin / Q000494:pharmacology; D012343:RNA, Transfer / Q000494:pharmacology; D012270:Ribosomes / Q000378:metabolism*; D013816:Thermodynamics
chemical_list: D001426:Bacterial Proteins; D011691:Puromycin; D012343:RNA, Transfer; D008034:Lincomycin; D000217:Acyltransferases; D010458:Peptidyl Transferases