SPECIFIC INACTIVATION OF PEPSIN BY A DIAZO KETONE

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Abstract
The diazo ketone L-l-diazo-4-phenyl-3-tosylamidobutanone (L-DPTB), in the presence of cupric ion, rapidly inactivates crystalline swine pepsin at pH 5.3 with parallel loss of enzymic activity toward hemoglobin and the synthetic substrate benzyloxy-carbonyl-L-histidyl-L-phenylalanyl-L-tryptophan ethyl ester. Complete inactivation is accompanied by the incorporation of one L-phenylalanyl residue (from the reagent) per pepsin molecule. Under comparable experimental conditions, L-DPTB does not react appreciably with pepsinogen or with alkali-denatured pepsin, indicating that the reagent specifically affects a group that is essential for the catalytic action of the enzyme. The D-isomer of the diazo ketone reacts with pepsin much more slowly than does the L-form. The inactivation of pepsin by the isomeric forms of DPTB is compared with the effect of L- and D-forms of diazoacetylphenylalanine ethyl ester, which in the presence of cupric ion rapidly inactivate pepsin but do not appear to exhibit the stereochemical discrimination found with the diazo ketone.

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