ISOTOPICALLY SENSITIVE REGIOSELECTIVITY IN THE OXIDATIVE DEAMINATION OF A HOMOLOGOUS SERIES OF DIAMINES CATALYZED BY DIAMINE OXIDASE

The equivalence of aminomethylene groups in selected diamine substrates of diamine oxidase was exploited for the determination of intramolecular isotope effects. In the series of substrates, [1,1-H-2(2)]-1,3-diaminopropane, [1,1-H-2(2)]-1,5-diaminopentane, [1,1-H-2(2)]-1,6-diaminohexane, [1,1-H-2(2)]-1,7-diaminoheptane and [alpha,alpha-H-2(2)]-4-(aminomethyl)benzylamine, the preference of the enzyme for reaction at the unlabeled methylene was found to vary from 1.45 to 10.5-fold. The observed partitioning ratios go through a minimum value with 1,5-diaminopentane, the best substrate of diamine oxidase of the compounds tested. The results suggest that fast substrates have less opportunity to reorient into alternate binding conformations while bound to the active site of the enzyme. On the other hand, diamine substrates tested that cannot exist in energetically favorable conformations with internitrogen distances of about 7 - 8 angstrom showed larger intramolecular isotope effects.