title: Binding of MET-TRNAf and GTP to homogeneous initiation factor MP.
abstract: Homogeneous initiation factor MP forms a stable complex with Met-tRNAf which binds to nitrocellulose filters in the absence of ribosomal subunits. Complex formation is rapid at 0 degrees and the rate of reaction is stimulated 20-fold by GTP when freshly prepared initiation factor MP is used. Under optimal assay conditions, a 1:1:1 stoichiometry for initiation factor MP, GTP, and Met-tRNAf is indicated, based on a molecular weight for initiation factor MP of 180,000. Kinetic analysis of ternary complex formation suggests an ordered reaction sequence with binding of GTP followed by binding of Met-tRNAf. However, binding of GTP appears to produce an unstable state which leads to rapid inactivation of initiation factor MP in the absence of Met-tRNAf. Formation of a stable binary complex of initiation factor MP and Met-tRNAf occurs in the absence of GTP. The binary complex cannot subsequently bind GTP. While storage of initiation factor MP at 0 degrees for several weeks has no effect on the rate or extent of Met-tRNAf binding in the presence of GTP, the rate of binary complex formation is increased 10-fold. The binary and ternary complexes appear to bind to 40 S ribosomal subunits with equal efficiency.
mesh_terms: D000818:Animals; D001665:Binding Sites; D004926:Escherichia coli; D006160:Guanosine Triphosphate / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000378:metabolism; D008274:Magnesium; D008715:Methionine; D010448:Peptide Initiation Factors; D010649:Phenylalanine; D011485:Protein Binding; D012343:RNA, Transfer / Q000378:metabolism*; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism
chemical_list: D010448:Peptide Initiation Factors; D010649:Phenylalanine; D006160:Guanosine Triphosphate; D012343:RNA, Transfer; D008715:Methionine; D008274:Magnesium