Takadiastase, adenosine aminohydrolase

Calf duodenal adenosine aminohydrolase affects enzymic hydrolysis of a wide variety of 6-substituted purine derivatives as well as analogs of adenosine with alteration in the purine ring and sugar moiety (Table IV) (65, 65a, 67, 70, 71, 112). Although not noted in Table IV, AMP, ADP, and ATP are not substrates. The hydrolysis of the 6-methoxy-purine derivative in H2180 occurs between C-6 and oxygen (113) consistent with the observed back incorporation of 180 from H2180 into inosine as catalyzed by both calf duodenal and Takadiastase non-... 

The reverse reaction, i.e., the direct conversion of inosine to adenosine catalyzed by both the calf duodenal and the Takadiastase nonspecific adenosine aminohydrolase (Section V) and measured as a function of pH with the calf enzyme, was defined by a theoretical curve for the equilibrium, K,= ([inosine] [NH i])/([adenosine] H20]) =38, with water concentration taken as one and pKa values of 8.8 and 9.2 for inosine and ammonium ion, respectively. The calculated AF = —5400 cal/mole at pH 7.0 was in reasonable agreement with —6000 cal/mole estimated from the summation of a series of partial reactions (114). 

Of the two homogeneous preparations of a nonspecific adenosine aminohydrolase from Aspergillus oryzae (Takadiastase) (92,179), that described by Wolfenden et al. (92) appears to be more facile and concise. Both procedures yield enzyme with turnover numbers near 105 moles adenosine deaminated per minute and molecular weights near 215,000. The mo-... 

Aspects of the mechanism of deamination catalyzed by the nonspecific Takadiastase enzyme are discussed in conjunction with calf duodenal adenosine aminohydrolase (see Section III). 

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