Abstract
1. Esters of γ-guanidino-l-α-toluene-p-sulphonamidobutyric acid (α-N-toluene-p-sulphonyl-l-norarginine) have been synthesized and shown to be hydrolysed by bovine trypsin and thrombin. As substrates for these enzymes, they were better than esters of α-N-toluene-p-sulphonyl-l-homoarginine or of α-N-toluene-p-sulphonyl-l-ornithine but not as good as esters of α-N-toluene-p-sulphonyl-l-arginine. 2. With trypsin as catalyst, the methyl and propyl esters are hydrolysed at the same rate at high substrate concentrations and hence deacylation of the acyl-enzyme appears to be rate-determining. In the presence of thrombin, however, the methyl ester is hydrolysed much faster than the n-propyl ester. 3. The variation of k0 with pH indicates that groups with pK(app.) values of 7·05±0·02 and 6·53±0·02 must be dissociated in trypsin and thrombin respectively for hydrolysis to proceed. 4. Activation constants have been determined for the trypsin-catalysed hydrolysis of methyl γ-guanidino-l-α-toluene-p-sulphonamidobutyrate and have been compared with the corresponding constants for the hydrolysis of homologous substrates. 5. Cholate increases k0 and decreases Km; the effects are more pronounced with thrombin than with trypsin.
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Selected References
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