<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>

Abstract

<img src='/image/spc_char/alpha.gif' border=0>-Chymotrypsin exhibits photoswitchable catalytic activities in aqueous solution after eight of its thirteen backbone amino groups are covalently attached via amide linkage to <i style="mso-bidi-font-style:normal">trans</i>-2-carboxyazobenzene [Ph-N=N-Ph-(<i style="mso-bidi-font-style:normal">o</i>-CO₂H), <b style="mso-bidi-font-weight:normal">1</b>]. Irradiation of

<i style="mso-bidi-font-style:normal">trans</i>-azo-analogue of the enzyme in phosphate buffer (<i style="mso-bidi-font-style:normal">p</i>H=7.6) at 314 nm gives the <i style="mso-bidi-font-style:normal">cis</i>-azo-analogue of the enzyme with a quantum efficiency of 0.14 at ambient temperature. The <i style="mso-bidi-font-style: normal">trans</i>→<i style="mso-bidi-font-style:normal">cis</i> photoreaction is reversed by irradiating the <i style="mso-bidi-font-style:normal">cis</i>-azo

enzyme at 430 nm. Both <i style="mso-bidi-font-style:normal">trans</i>-and <i style="mso-bidi-font-style:normal">cis</i>-forms of the azo-enzyme catalyze the hydrolysis of <i style="mso-bidi-font-style:normal">p</i>-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

<span style="font-size:12.0pt;font-family:" times="" new="" roman";="" mso-fareast-font-family:"times="" roman";mso-ansi-language:en-in;mso-fareast-language:="" en-in;mso-bidi-language:ar-sa"="" lang="EN-IN">hydrolysis rate of unmodified enzyme is found to be 8.97 × 10⁴ moles/min. The photoisomerizable awbenzene units of <b style="mso-bidi-font-weight:normal">1</b> effect perturbation in the structure of <img src='/image/spc_char/alpha.gif' border=0>-chymotrypsin, thereby offering a convenient method to control its substrate binding affinity and hence its catalytic activity.</span></span></span></span>