Studies in enzymatic peptide synthesis

Typescript (photocopy).Chapter I. The incorporation of D-amino acids into peptides via kinetic approach enzymatic peptide synthesis is examined. D-amino acid esters were found to be fairly efficient acyl-acceptors under conditions of high organic cosolvent. Various parameters effecting peptide yield are examined, such as nucleophile concentration# enzyme concentration# temperature, type and concentration of cosolvent, and enzyme immobilization. A novel type of amino-acid analog, a-nitro, a-methyl acids, is found to be a moderately efficient acyl-donor, with D-specificity. Chapter II. As a method for avoiding potential secondary hydrolysis of peptide products in protease-catalyzed peptide synthesis# various lipases lacking amidase activity are examined as catalysts in peptide synthesis. While synthesis does occur# reaction times are sluggish and it is found to be difficult to minimize hydrolysis of the acyl-donor ester. Chapter III. The chemical modification of proteases to esterases to achieve a peptide synthesis catalyst without amidase activity is examined. (His[95])N-methyl Chymotrypsin is synthesized and found to be very effective in peptide synthesis, while completely lacking the amidase activity. Chapter IV. Techniques are developed for determining nucleophile affinity in protease catalyzed peptide synthesis. This not only allows quantification of nucleophile specificity, which may be different from hydrolytic leaving group specificty, it allows for changes in active site architecture due to chemical or genetic alteration to be mapped