Quinocofactors in Copper Amine Oxidases and Lysyl Oxidase

Abstract

Although quinones have been recognized as electron transfer reagents in biology, they had not been considered as important redox cofactors. However, this view has changed over the past five years with the emergence of the field of quinoproteins (J.P. Klinman, D. Mu, 1994). The first quinone to be described was pyrroloquinoline quinone (PQQ), which has been carefully documented to function as a dissociable cofactor in gram negative bacteria (cf. S.A. Salisbury et al., 1979). The PQQ-utilizing proteins are alcohol dehydrogenases, which are found in the periplasmic space of gram negative bacteria and often observed in greater quantities than the cofactor itself. This latter property has led to the observation that PQQ can function as a stimulant/vitamin when present in the growth medium of certain bacteria (M. Shimao et al., 1984; M. Ameyama et al., 1984).