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.

Arylamidase of Neisseria catarrhalis

Neisseria catarrhalis produces arylamidase intracellularly and is one of the gram-negative bacteria producing exceptionally large amounts of this enzyme. In general, gram-positive bacteria do not produce this enzyme. Arylamidase from N. catarrhalis was purified by salt fractionation, chromatography, and density gradient ultracentrifugation. Its sedimentation coefficient was 6.6; l-alanine-beta-naphthylamide (betaNA) was the most rapidly hydrolyzed amino acid-betaNA. The enzyme had pK(e) values of 6.1 and 8.7 and pK(es) values of 7.1 and 7.9; only those amino acid-betaNA compounds of the l configuration were susceptible to hydrolysis. Arylamidase catalyzed stepwise hydrolysis of dipeptide-betaNA, beginning with the N-terminal residue. Substrates having amino acid residues with larger R groups, such as leucine, interacted much more effectively with enzyme. The significance of the predominate occurrence of arylamidase activity in gram-negative bacteria and the role of this enzyme in the physiology of these organisms remain unclear. It has been established, however, that arylamidase is distinct from leucine aminopeptidase.