Specific interaction of guanidine hydrochloride with essential carboxyl group of xylanase from alkalothermophilic Bacillus sp.

Experimental evidence for the specific interaction of guanidine hydrochloride with the carboxyl group of xylanase has been presented for the first time. Guanidine hydrochloride (0.1 M) inactivated the xylanase from alkalothermophilic Bacillus sp. to 50% without affecting the conformation of the protein as determined by the fluorometric profile. The kinetic analysis indicated a competitive type of inhibition and a requirement of 1.4 molecules of guanidine hydrochloride per molecule of the enzyme for inhibition. Maximum inhibition occurred at the pH which is optimum for the enzyme activity. The reaction of guanidine hydrochloride with the enzyme prior to modification by Woodward's Reagent K, a specific inhibitor of the carboxyl group, made it inaccessible for modification as indicated by absorbance data at 340 nm. Urea, sodium dodecyl sulphate, LiCl, KCl and NaCl at 0.1 M concentration each had negligible effect on the enzyme activity.