Kinetic specificities of BPN' and Carlsberg subtilisins. Mapping the aromatic binding site.
The kinetic specificities of BPN' and Carlsberg subtilisins [EC 3.4.21.14] were examined with various nucleus-substituted derivatives of Nalpha-acetylated aromatic amino acid methyl esters for mapping their hydrophobic binding sites in comparison with that of alpha-chymotrypsin. The Carlsberg enzyme was generally much more reactive than the BPN' enzyme due to the larger kcat value. The fact that the two sutilisins hydrolyzed Ac-Tyr(PABz)-OMe, which is a derivative of tyrosine bearing a planar trans-p-phenylazobenzoyl group at the OH-function, with the smallest Km value showed that these enzymes possess a more extended aromatic binding site than has so far been demonstrated. Ac-Phe(4-NO2)-OMe was remarkable in being hydrolyzed with a particularly large kcat value (5,500 +/- 700 s-1 at pH 7.8 for Carlsberg subtilisin). Ac-Phe(4-NO2)-OMe and Ac-Tyr-OMe were distinguished by Carlsberg subtilisin in terms of kcat but not by BPN' subtilisin, suggesting that the specificity site of the former is more sensitive to a small change in size of substituent than that of the latter. Ac-Trp(NCps)-OMe and Ac-Trp(NCps)-OH were bound to the enzyme's active site but in a competitive manner. A difference in the standard free energies of binding between the two enzymes may indicate that the hydrophobic cleft of Carlsberg subtilisin is somewhat deeper and/or narrower than that of BPN' subtilisin.
D001407:Bacillus / Q000201:enzymology; D001412:Bacillus subtilis / Q000201:enzymology; D001665:Binding Sites; D002918:Chymotrypsin / Q000378:metabolism; D006868:Hydrolysis; D007700:Kinetics; D013045:Species Specificity; D013379:Substrate Specificity; D013381:Subtilisins / Q000037:antagonists & inhibitors / Q000378:metabolism*
D013381:Subtilisins; D002918:Chymotrypsin