title: S-adenosylhomocysteine metabolism in various species.
abstract: Eleven microorganisms, four plants, and major organs from the chicken, dog, rat and rabbit were assayed for the presence of S-adenosylhomocysteine hydrolase, S-adenosylhomocysteine nucleosidase, and S-ribosylhomocysteine-cleavage enzyme. All bacteria (procaryotes) were found to possess S-adenosylhomocysteine nucleosidase and S-ribosylhomocysteine-cleavage enzyme but not S-adenosylhomocysteine hydrolase; All eucaryotes tested, including yeasts, plants, birds, and mammals, possessed S-adenosylhomocysteine hydrolase but not S-adenosylhomocysteine nucleosidase or S-ribosylhomocysteine-cleavage enzyme. Of all the organs assayed in the vertebrates, the level of S-adenosylhomocysteine hydrolase was highest in liver, pancreas, and kidney, lower spleen and testis, and very low in brain and heart; In all systems tested, equilibrium of the hydrolase reaction always favored synthesis over hydrolysis. We studied some of the kinetic properties of the hydrolase from rat liver; In the direction of synthesis, the Km value was 1.5 mM for adenosine and 4.5 mM for L-homocysteine, whereas marked substrate inhibition was observed with L-homocysteine. The condensation reaction is subject to product inhibition, and was inhibited by adenine. Results from in-vivo experiments revealed that the cells of the various organs of the dog are impermeable to the exogenously administered S-adenosylhomocysteine.
mesh_terms: D000241:Adenosine / Q000378:metabolism*; D000818:Animals; D001419:Bacteria / Q000378:metabolism; D002645:Chickens; D004285:Dogs; D005658:Fungi / Q000378:metabolism; D006710:Homocysteine / Q000378:metabolism*; D007700:Kinetics; D009699:N-Glycosyl Hydrolases / Q000378:metabolism; D009928:Organ Specificity; D010944:Plants / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D013045:Species Specificity
chemical_list: D006710:Homocysteine; D009699:N-Glycosyl Hydrolases; D000241:Adenosine