Abstract
Summary
1. A purified cathepsin III (leucine aminopeptidase) preparation hydro-lyzed L-leucinamide from 2 to 3 times as fast as either L-leucylglycine or L-leucyl-γ-amino-butyric acid and about 4 times as fast as L-leucyl-β-alanine. The activity of the enzyme was not affected by the proximity to the peptide bond of the free carboxyl group of leucyl peptides. 2. The fact that L-leucinamide is hydrolyzed faster than are the peptides of leucine can possibly be explained by the hypothesis that the large groups attached to the peptide nitrogen of the substrates interfere with the formation of an enzyme-substrate complex. 3. The hydrolysis of the substrates by enzyme preparation A closely approximated zero order kinetics. The failure to observe a regular kinetic order for the reactions catalyzed by preparations B and C may be the result of destruction of the enzyme in the more highly purified preparations.
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