title: Methionyl-tRNA synthetase from sheep mammary gland. Purification of a fully active monomeric enzyme derived from high-molecular-weight complexes by controlled proteolysis.
abstract: Methionyl-tRNA synthetase from sheep lactating mammary gland is found predominantly in the form of high-molecular-weight complexes. Controlled proteolysis of these aggregates generates a low-molecular-weight species of the enzyme with full maintenance of activity as assessed by the rate of aminoacylation of tRNA. The product of proteolysis, which has been purified to homogeneity with a yield of 23%, is a monomeric enzyme of molecular weight 78 000. It has a specific activity of 405 units/mg at 25 degrees C. These findings clearly demonstrate that the aggregated state of methionyl-tRNA synthetase is not a prerequisite for full expression of catalytic activity. Furthermore, the results emphasize the need to provide effective protection against proteolytic damage in studies dealing with the characterization of high-molecular-weight complexes of aminoacyl-tRNA synthetases.
mesh_terms: D000604:Amino Acyl-tRNA Synthetases / Q000302:isolation & purification*; D000818:Animals; D002846:Chromatography, Affinity; D005260:Female; D007774:Lactation; D008321:Mammary Glands, Animal / Q000201:enzymology*; D008718:Methionine-tRNA Ligase / Q000302:isolation & purification*; D008970:Molecular Weight; D011247:Pregnancy; D011485:Protein Binding; D012756:Sheep
chemical_list: D000604:Amino Acyl-tRNA Synthetases; D008718:Methionine-tRNA Ligase