The relative effectiveness of guanidinium and some biguanide salts as denaturants. Assessment against penicillinase.

Penicillinase (penicillin amido-beta-lactamhydrolase, EC 3.5.2.6) has been used as a model for quantitating the effectiveness of several guanidine-derived denaturants. It was chosen because the mechanism of its denaturation by urea and guanidinium chloride has been worked out in detail, because it has a low thermodynamic stability bringing it in the range of weak denaturants, and because its denaturation can readily be followed by enzyme activity as well as by spectroscopic probes. Contrary to previous reports, biguanide HCl is found to be no more effective than guanidinium chloride. The denaturant effectiveness of the various compounds studied is found to increase in the order: guanidinium chloride identical to biguanide HCl less than propylbiguanide HCl less than hexylbiguanide HCl much less than n-decylbiguanide HCl. n-Decylbiguanide HCl is a particularly powerful denaturant, unfolding penicillinase at a concentration of less than 0.015 M.