Partial purification and properties of adenosine nucleosidase from leaves of spinach beet (Beta vulgaris L.).

Adenosine nucleosidase (EC 3.2.2.7), which catalyses the irreversible hydrolysis of adenosine to adenine and ribose, has been isolated and purified about 40-fold from leaves of spinach beet (Beta vulgaris L.). The enzyme appeared to be specific for adenosine only among the naturally-occurring nucleosides, but comparable activity was also found with adenosine N-oxide. Adenosine hydrolysis, which had an optimum at pH 4.5, did not require phosphate ions nor was it stimulated by their presence. The Michaelis constant for this substrate was 11 μM. Whereas the rate of adenosine hydrolysis was unaffected by DL-homocysteine, L-methionine and ribose, it was sensitive to the presence of adenine, S-adenosyl-L-methionine, S-adenosyl-L-homocysteine, AMP and deoxyadenosine. The role of this enzyme in plant metabolism is discussed.