Abstract
Adenosylhomocysteinase (EC 3.3.1.1)-catalyzed hydrolysis of adenosylhomocysteine was measured in 0.1M HEPES, pH 7.0, at 37°C by continuous monitoring of the reaction product at 265 nm in the presence of adenosine deaminase. The initial reaction rate was a hyperbolic function of substrate concentration. The apparent Km (60 uM) decreased upon addition of phosphate ions (Pi), reaching an asymptotic value of 20 uM in the presence of an excess of Pi (half saturation value = 8 mM Pi). The apparent Vmax seemed to be unaffected by Pi. Pyrophosphate, arsenate, and sulfate exerted similar effects. Upon addition of 20-50 mM mercaptoethanol (but not ethylene glycol, ethanol, or glycerol), not only was the initial reaction rate lowered, but the hydrolysis process came to a stop without even reaching completion. Upon addition of new enzyme to the reaction mixture, there was further hydrolysis of the residual adenosylhomocysteine; no activity was instead restored if new adenosylhomocysteine was added to the inactivated enzyme. In the same concentration range, mercaptoethanol per se was totally ineffective on the enzyme in the absence of substrate.
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Salerno, C., Bozzi, A., Crifò, C. et al. KINETIC PROPERTIES OF HUMAN ERYTHROCYTE ADENOSYLHOMO CYSTEINASE: 177. Pediatr Res 19, 773 (1985). https://doi.org/10.1203/00006450-198507000-00197
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DOI: https://doi.org/10.1203/00006450-198507000-00197