ESSENTIAL GROUPS AT THE ACTIVE SITE OF 7?RAPAEOLUM INVERTASE

MARIA INES ISLA, MARTA AMELIA VATTUONE* ANTONIO RODOLFO SAMPRETRO

PHYTOCHEMISTRY

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 1998 vol. 47 p. 1189 - 1193

0031-9422

ino acid residues involved at the active site of Tropaeolum r?uzjus invertase (p-D-fructofuranosidefructohydrolase. EC 3.2.1.26) were determined. Photo-oxidation and Woodward?s reagent K revealed thepresence of histidyl and carboxylic groups at the active site of the enzyme. These groups were protected bysucrose and trehalose but not by fructose. Thiol groups were determined with sodiump-chloromercuribenzoateand with 5,5?-dithio-his(2-nitrobenzoic acid). These groups were protected by fructose and to a lesser degreeby sucrose, but were not protected by trehalose. The pH dependence of I?,,,?,,,a nd K,,, at 27? and 37 ? is consistentwith the presence of carboxyl and histidyl residues at the invertase active site. The pK, values obtainedcorrespond to ionization heats of 1700 cal mol-? and 6820 cal mol-?. The results were consistent with thepresence of imidazole, carboxylic and thiol groups at the active site.