Abstract-DAO was partially purified from hog kidney by a procedure involving differential centrifugation, heat treatment and ammonium sulfate fractionation.The enzymic properties of partially purified DAO were studied with cadaverine and hista mine as substrates and the following results were obtained.The specific activities of hog kidney DAO at the final step of purification were 183-fold and 125-fold those of the crude homogenate with histamine and cadaverine, respectively, as substrates. With cadaverine and histamine the pS maxima values were 3×10-3 M and 1×10-3 M and the pH optima were 7.1 and 6.5, respectively. All the diamines tested, (i.e. cadaverine, putrescine, hexamethylenediamine, histamine, ethylenediamine and agma tine) were oxidized with this enzyme, while monoamine, (i.e. tyramine, benzylamine, serotonin, β-phenylethylamine, n-amylamine and n-propylamine) were not. DAO activity was inhibited by aminoguanidine, hydroxylamine, MPH and semicarbazide. The inhibitory effects were similar when either cadaverine or histamine was used as substrate. SH-reagents, such as PCMB and iodoacetoamide, did not affect DAO activity, but various metal ions, such as CuCl, Cu(NO3)2, Zn(NO3)2, AICl3 and Fe (NO3)3 were inhibitory. The inhibitory effect of AgNO3 on DAO activity differed greatly, when using cadaverine and histamine as substrates. The temperature-in -activation curves of DAO measured with cadaverine and with histamine were different.There have been reports on diamine oxidase (DAO) (E.C. 1.4.3.6. diamine: oxygen oxydoreductase (deaminating)), which catalyzes the oxidation of cadaverine, putrescine and agmatine, and histaminase which catalyzes the oxidation of histamine. Since the substrate specificities of DAO and histaminase are very similar (1-6), Zeller called both enzymes DAO. Goryachenkova (7) and Leloir (8) also suggested that DAO and hista minase were the same enzyme because they could not be separated by electrophoresis .Mondovi et al. (9) also stated that these two enzymes were identical since during purifica tion the ratio of the activities in oxidation of cadaverine and histamine remained almost the same. On the other hand, Kapeller-Adler (10-11) reported that DAO and histaminase were different enzymes, since her histaminase preparation purified from hog kidney oxidized histamine but not cadaverine.Thus although there have been many investigations on the possible identity of these two enzymes, the problem has yet to be clarified. In the present work the amine oxidase was partially purified from hog kidney, and the properties were studied using cadaverine and histamine as substrates.
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