Evidence against a temperature-dependent conformational change in urocanase from Pseudomonas putida

Abstract

Enzymatic activity of urocanase )4-imidazolone-5-propionate hydro-lyase, EC 4.2.1.49) has an unusual resistance to temperature changes, and a temperature-dependent conformational change has been suggested (Hug, D.H. and Hunter, J.K. (1974) Biochemistry 13, 1427–1431). A conformational change or dissociation has been proposed in the range 29–31°C (Cohn, M.S., Lynch, M.C. and Phillips, A.T. (1975) Biochim. Biophys. Acta 377, 444–453). In this work no evidence was found for a temperature-dependent conformational change or dissociation. Arrhenins plots of K m and V max were linear; the sedimentation coefficient was independent of temperature; tryptophanyl fluorescence was a linear function of temperature; and heat capacity calorimetry showed no transitions below 60°C.