<span style="font-size:12.0pt;font-family: "Times New Roman";mso-fareast-font-family:"Times New Roman";mso-ansi-language: EN-IN;mso-fareast-language:EN-IN;mso-bidi-language:AR-SA" lang="EN-IN">Photocontrol of <img src='/image/spc_char/alpha.gif' border=0>-chymotrypsin activity by covalently linked 2-carboxyazobenzene units</span>

885-888-Chymotrypsin exhibits photoswitchable catalytic activities in aqueous solution after eight of its thirteen backbone amino groups are covalently attached via amide linkage to trans-2-carboxyazobenzene [Ph-N=N-Ph-(o-CO2H), 1]. Irradiation of trans-azo-analogue of the enzyme in phosphate buffer (pH=7.6) at 314 nm gives the cis-azo-analogue of the enzyme with a quantum efficiency of 0.14 at ambient temperature. The <i style="mso-bidi-font-style: normal">trans→cis photoreaction is reversed by irradiating the cis-azo enzyme at 430 nm. Both trans-and cis-forms of the azo-enzyme catalyze the hydrolysis of p-nitrophenyl acetate and the rates of this light-induced hydrolysis are found to be 7.77 and 6.98 (×104) mol / min respectively. Under similar conditions the hydrolysis rate of unmodified enzyme is found to be 8.97 × 104 moles/min. The photoisomerizable awbenzene units of 1 effect perturbation in the structure of -chymotrypsin, thereby offering a convenient method to control its substrate binding affinity and hence its catalytic activity.</span