title: Modification of phenylalanyl-tRNA synthetase from baker's yeast by proteolytic cleavage and properties of the trypsin-modified enzyme.
abstract: Earlier studies have shown that native phenylalanyl-tRNA synthetase from baker's yeast contains two different kinds of subunits, alpha of molecular weight 73000 and beta of molecular weight 63000. The enzyme is an asymmetric tetramer alpha-2beta-2, which binds two moles of each ligand per mole. Incubation of the purified enzyme with trypsin results in an irreversible conversion: the alpha-subunit remains apparently unchanged but beta is rapidly degraded and yields a lighter species beta of molecular weight 41000. The trypsin-modified enzyme is an alpha-2beta-2 molecule which can still activate phenylalanine but cannot transfer it to tRNA-Phe; furthermore it does not bind tRNA-Phe but its kinetic parameters are identical to those of the native enzyme with respect to ATP and phenylalanine. Therefore the two beta subunits play a critical part in tRNA binding. Isolated alpha or beta subunits exhibit no significant activity and both types of subunit seem to be required for phenylalanine activation.
mesh_terms: D000255:Adenosine Triphosphate; D000604:Amino Acyl-tRNA Synthetases; D001665:Binding Sites; D011756:Diphosphates; D004591:Electrophoresis, Polyacrylamide Gel; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D010652:Phenylalanine-tRNA Ligase / Q000378:metabolism; D011485:Protein Binding; D012343:RNA, Transfer; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D013997:Time Factors; D046249:Transfer RNA Aminoacylation; D014357:Trypsin
chemical_list: D011756:Diphosphates; D046911:Macromolecular Substances; D000255:Adenosine Triphosphate; D012343:RNA, Transfer; D014357:Trypsin; D000604:Amino Acyl-tRNA Synthetases; D010652:Phenylalanine-tRNA Ligase