Morphine metabolism in the opium poppy and its possible physiological function - Biochemical characterization of the morphine metabolite, bismorphine

We identified a novel metabolic system of morphine in the opium poppy (Papa ver somniferum L.). In response to stress, morphine is quickly metabolized to bismorphine consisting of two morphine units, followed by accumulation i n the cell wall. This bismorphine binds predominantly to pectins, which pos sess high galacturonic acid residue contents, through ionical bonds. Our ne wly developed method using artificial polysaccharides demonstrated that bis morphine bridges are formed between the two amino groups of bismorphine and the carboxyl groups of galacturonic acid residues, resulting in crosslinki ng of galacturonic acid-containing polysaccharides to each other. The abili ty of bismorphine to cross-link pectins is much higher than that of Ca2+, w hich also acts as a cross-linker of these polysaccharides. Furthermore, we confirmed that cross-linking of pectins through bismorphine bridges leads t o resistance against hydrolysis by pectinases. These results indicated that production of bismorphine is a defense response of the opium poppy. Bismor phine formation is catalyzed by anionic peroxidase that pre-exists in the c apsules and leaves of opium poppies. The constitutive presence of morphine, together with bismorphine-forming peroxidase, enables the opium poppy to r apidly induce the defense system.