title: S-Adenosylhomocysteinase from yellow lupin seeds: stoichiometry and reactions of the enzyme-adenosine complex.
abstract: Plant (Lupinus luteus) S-adenosylhomocysteinase, an alpha 2 dimer, forms a 1:2 enzyme-adenosine complex. The binding sites for adenosine are not equivalent. Binding of the first molecule of adenosine is fast (k greater than 7 x 10(5) M-1 s-1), whereas the second molecule of adenosine binds in a slow process with a half-life of 5 min. Adenosine in the 1:1 and 1:2 enzyme--substrate complexes reacts slowly (k = 0.05 min-1) to give finally free enzyme, adenine, and ribose. The enzyme does not lose its ability to catalyze the synthesis of S-adenosylhomocysteine during the reactions. The relevance of the data to the catalytic functioning of the plant S-adenosylhomocysteinase is discussed.
mesh_terms: D000241:Adenosine; D043383:Adenosylhomocysteinase; D001665:Binding Sites; D006867:Hydrolases / Q000378:metabolism*; D007700:Kinetics; D011485:Protein Binding; D012435:S-Adenosylhomocysteine; D012639:Seeds / Q000201:enzymology*
chemical_list: D012435:S-Adenosylhomocysteine; D006867:Hydrolases; D043383:Adenosylhomocysteinase; D000241:Adenosine