A method for the determination of some amino acid decarboxylases.

Mammalian organs are known to decarboxylate a number of n-amino acids. Of the mammalian decarboxylases, 3,4-dihydroxyphenylalanine decarboxylase is probably the most studied. Blaschko (1) reported values for DOPAl decarboxylase in .liver and kidney of several animal species. The enzyme was shown to be deactivated by dialysis and its activity restored by the addition of pyridoxal phosphate (2, 3). Interest in DOPA decarboxylase has increased. New studies of the properties of thii enzyme have been reported (4,5). Some preparations of DOPA decarboxylase act upon other substrates. Blaschko (6) has shown that o-tyramine could be formed from o-tyrosine in the animal. He has also demonstrated that the enzyme can act on m-tyrosine but not on p-tyrosine (7). With the discovery of 5-hydroxytryptophan decarboxylase, the problem has become more complex. This enzyme appears to be difficult to separate from DOPA decarboxylase (8). The method most frequently used to measure DOPA decarboxylase and other amino acid decarboxylases has been manometric. Unfortunately the measurement of CO2 is not sufficiently sensitive to permit measurement of low activities. Measurement of the resulting product, the amine, could increase the range considerably. This is done in many cases; the amine is measured by physical, chemical, or biological methods. Dietrich (9) has used Permutit successfully to separate the amine from the amino acid and presented a rapid method for the determination of DOPA decarboxylase. Recently we reported (10) that Amberlite CG-50 H+ can separate amino acids and amines quantitatively and proposed the use of this procedure as a method for measuring ammo acid decarboxylases. We are reporting the details of the method in this paper. With the method reported, we have measured four decarboxylases, viz. o-tyrosine, m-tyrosine, 3,4-dihydroxyphenylalanine, and 5-hydroxytryptophan. Eight different organs from three different animal species were studied and all were found to possess activity with all four substrates.