A chromophore in glutamate decar☐ylase has been wrongly identified as PQQ

Abstract
Pyrroloquinoline quinone (PQQ) has been claimed to be a component of glutamate decar☐ylase fromEscherichia coli on the basis of a frequently used procedure in which the protein is extracted with hexanol. We demonstrate that if pyridoxal phosphate (PLP) is not added during the preparation, the apoenzyme prepared from glutamate decar☐ylase contains no chromophore absorbing above 280 nm. Full enzyme activity and the original holoenzyme spectrum are restored by the addition of PLP alone, A 340 nm-absorbing band, similar to that which prompted analysis for PQQ, is produced by exposure of the enzyme to solutions of PLP