Fuculose-1-phosphate aldolase of Methanococcus jannaschii: Reaction of histidine residues connected with catalytic activities

Abstract

The enzyme Fuc aldolase from Methanococcus jannaschii that catalyzes the aldol condensation of DRAP and L-lactaldehyde to give fuculose-1-phosphate was inactivated by DER The inactivation was pseudo first-order in the enzyme and DEP, which was biphasic. A pseudo second-order rate constant of 120 M-1-min(-1) was obtained at pH 6.0 and 25 degreesC. Quantifying the increase in absorbance at 240 nm showed that four histidine residues per subunit were modified during the nearly complete inactivation. The statistical analysis and the time course of the modification suggested that two or three histidine residues were essential for activity. The rate of inactivation was dependent on the pH, and the pH inactivation data implied the involvement of an amino acid residue with a pK(a) value of 5.7. Fuc aldolase was protected against DEP inactivation by DHAP, indicating that the histidine residues were located at the active site of Fuc aldolase. DL-Glyceraldehyde, as an alternative substrate to L-lactaldehyde, showed no specific protection for Fuc aldolase.