The C-S lyases of higher plants: homogeneous beta-cystathionase of spinach leaves.
S-Substituted cysteines and their derivatives are prominent secondary amino acids in a number of plant families. The substituents are often specific and unique to each family. Cystathionine, however, is an ubiquitous S-substituted cysteine found in all autotrophic plants since it is an intermediate in the biosynthesis of methionine. beta-Cystathionase will produce homocysteine and pyruvate from cystathionine by a beta-elimination reaction. The present report describes the purification of this enzyme to homogeneity from spinach leaves and some of its properties. The enzyme has a molecular weight of 210,000 and consists of four identical subunits of Mr 53,000. It has a pH optimum for activity of 8.6-8.7 and utilizes pyridoxal-5'-phosphate as a cofactor. Its specificity is limited to L-cystathionine, L-djenkolate, and L-cystine as substrates with a relative activity of 100:126:17, respectively. It is not a glycoprotein unlike a number of previously described plant C-S lyases.
Staton
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Department of Food Science and Technology, University of California, Davis 95616.
Mazelis
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D000596:Amino Acids / Q000032:analysis; D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008190:Lyases / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism; D008970:Molecular Weight; D010944:Plants / Q000201:enzymology*; D011487:Protein Conformation; D013379:Substrate Specificity; D013816:Thermodynamics
D000596:Amino Acids; D008190:Lyases; C019965:cystathionine beta-lyase