The distribution of aminoacylase I among mammalian species and localization of the enzyme in porcine kidney

Aminoacylase I (Acy-1, EC 3.5.1.14) is found in many mammalian tissues, wit h highest activities occurring in kidney. The enzyme hydrolyzes a variety o f N-acylated amino acids; however, the physiological role and the exact cel lular localization of Acy-1 are still a matter of debate. The comparison of Acy-1 activities in kidney and liver homogenates of 11 mammalian species s howed that the enzyme is most abundant in true herbivores such as sheep and cattle as well as in omnivores, while activities were very low in both rod ents and the cat. Acy-1 activity was not detected in livers of dogs of five different breeds. Using in situ hybridization of porcine kidney sections w ith DIG-labeled RNA probes, Acy-1 mRNA was shown to be evenly distributed t hroughout the tubular system, while glomeruli and the interstitium were fre e of stain. During subcellular fractionation, porcine Acy-1 behaved like a typical cytosolic enzyme. Commonly, Acy-1 is thought to catalyze hydrolytic reactions, i.e., the formation of free amino acids from acylated derivativ es. Based on the present results and literature data, we propose a novel hy pothesis, i.e., that Acy-1 catalyzes the synthesis (rather than the hydroly sis) of hippurate that is formed as a detoxification product of aromatic co mpounds. (C) 2000 Societe francaise de biochimie et biologie moleculaire / Editions scientifiques et medicales Elsevier SAS.