S-Adenosyl-L-Homocysteine Hydrolase

The enzymatic activity that catalyzes the reversible hydrolysis of S-adenosyl-L -homocysteine (AdoHcy) to L -homocysteine (Hey) and adenosine (Ado), or, in reverse, the formation of AdoHcy from Hcy and Ado, is known as AdoHcy hydrolase (AHH) (EC 3.3.1.1). Another name for it, obviously, although rarely used, is AdoHcy synthase. The activity was first described as a single enzymatic entity by (1959 ), although it was known since 1955 that AdoHcy undergoes enzymatic breakdown when incubated with crude rat liver extracts (Ericson et al., 1955 ). In that same year AdoHcy was chemically characterized as the product derived from S-adenosyl-L -methionine (AdoMet) via transmethylation (Baddiley and Jamieson, 1955 ), a reaction first revealed by the pioneering studies of (1954 ) The reaction catalyzed by AHH has been extensively examined and its role in cellular biology across species and phyla (Finkelstein, 1971 ; Duerre and Walker, 1977 ) dealt with on several occasions. The role of this enzyme in transmethylation reactions taking place in cells of the nervous system has also been examined (Schatz et al., 1979 ), although no comprehensive treatment of this facet of AHH action exists Yet, information on brain AHH has been summarized (Sellinger and Schatz, 1979 ) in a monograph devoted to the role of AdoMet in the CNS (Zappia et al., 1979 ).