Brain arylamidase. Purfication and characterization of the soluble bovine enzyme.

1. An enzyme acting on aminoacyl-beta-naphthylamides has been isolated from the soluble fraction of bovine brain and purified 205-fold by means of ammonium sulphate fractionation, hydroxyapatite adsorption and DEAE-Sephadex column chromatography. 2. Arylamidase requires thiol groups for retention of its activity, is heat-labile and is susceptible to freezing. p-Chloromercuribenzoate and N-ethylmaleimide inactivate the enzyme rapidly. 3. Metal ions are not required for its activity, but stimulation by Mn(2+) and Mg(2+) and inactivation by Co(2+) and Zn(2+) are observed. 4. Optimum pH7.5 in phosphate buffer was exhibited for all substrates tested except l-leucyl-beta-naphthylamide, for which optimum pH is 6.5. 5. K(m) values for a number of substrates have been obtained and substrate inhibition at high concentrations was demonstrated. 6. The molecular weight is approx. 70000 as determined by Sephadex-gel filtration.