Two histidine residues are essential for catalysis by lecithin retinol acyl transferase

Lecithin retinol acyl transferase (LRAT) is a novel membrane bound enzyme t hat catalyzes the formation of retinyl esters from vitamin A and lecithin. The enzyme is both essential for vision and for the general mobilization of vitamin A. The sequence of LRAT defines it as a novel enzyme unrelated to any other protein of known function. LRAT possesses a catalytically essenti al active site cysteine residue. The enzyme also contains six histidine res idues. It is shown here that two of these residues (H57 and H163) are essen tial for catalysis. A mechanistic hypothesis is presented to account for th ese observations. (C) 2001 Federation of European Biochemical Societies. Pu blished by Elsevier Science B.V. All rights reserved.