Hydrolysis of amino acid amides of dopamine by extracts of animal tissues.

Abstract An investigation was made of the in vitro hydrolysis of numerous amides of dopamine (DA) and its α- or O -methylated derivatives with α-amino acids. These amides were hydrolyzed by aminoacylarylamidase, and they exhibited a wide spectrum of hydrolysis rates when incubated at pH 6.9 with the particulate fraction of renal homogenates. l -Alanyl-DA ( l -ADA) was the most rapidly hydrolyzed of all the amides tested with canine kidney, and the l -alanyl amide of each derivative of DA was also preferentially hydrolyzed. Relative rates ranged from a value of 1.000 for l -ADA to 0.002 for l -prolyl-DA; very few amides were not hydrolyzed at all. Amidase activity against l -ADA was very high in the small intestine and kidney; plasma contained less activity and that of other tissues was negligible. When tested against a small series of DA-amides, amidase preparations of canine duodenum, kidney, and plasma showed identical specificities. Species differences do exist, however, because crystalline renal arylamidase of the pig and unpurified renal amidases of the rat, dog, monkey and human showed minor differences in substrate specificity.