MODIFICATION OF TOMATO AND ASPERGILLUS-NIGER PECTINESTERASES WITH DIETHYL PYROCARBONATE

The role of histidine residues in pectinesterases was evaluated by mon itoring the sensitivity to modification with diethyl pyrocarbonate in the tomato and Aspergillus niger enzymes. Different and incomplete los ses of enzyme activity were obtained. Inactivation of the enzymes was proportional to the histidine content (two in the tomato T1 form, Six in the Aspergillus form), suggesting that accessible histidine residue s do not have active-site functions in these pectinesterases, but cont ribute to the overall structural stability. Lack of His roles in commo n between the enzyme forms is in agreement with the structures of pect inesterases having no conserved His residues.