MANGANESE-DEPENDENT CLEAVAGE OF NONPHENOLIC LIGNIN STRUCTURES BY CERIPORIOPSIS-SUBVERMISPORA IN THE ABSENCE OF LIGNIN PEROXIDASE

Many ligninolytic fungi appear to lack lignin peroxidase (LiP), the en zyme generally thought to cleave the major, recalcitrant, nonphenolic structures in lignin, At least one such fungus, Ceriporiopsis subvermi spora, is nevertheless able to degrade these nonphenolic structures, E xperiments showed that wood block cultures and defined liquid medium c ultures of C. subvermispora rapidly depolymerized and mineralized a C- 14-labeled, polyethylene glycol-linked, high-molecular-weight beta-O-4 lignin model compound (model I) that represents the major nonphenolic structure of lignin, The fungus cleaved model I between C-alpha and C -beta to release benzylic fragments, which were shown in isotope trapp ing experiments to be major products of model I metabolism, The C-alph a-C-beta cleavage of beta-O-4 lignin structures to release benzylic fr agments is characteristic of LiP catalysis, but assays of C. subvermis pora liquid cultures that were metabolizing model I confirmed that the fungus produced no detectable LiP activity, Three results pointed, in stead, to the participation of a different enzyme, manganese peroxidas e (MnP), in the degradation of nonphenolic lignin structures by C, sub vermispora, (i) The degradation of model I and of exhaustively methyla ted (nonphenolic), C-14-labeled, synthetic lignin by the fungus in liq uid cultures was almost completely inhibited when the Mn concentration of the medium was decreased from 35 mu M to approximately 5 mu M. (ii ) The fungus degraded model I and methylated lignin significantly fast er in the presence of Tween 80, a source of unsaturated fatty acids, t han it did in the presence of Tween 20, which contains only saturated fatty acids, Previous work has shown that nonphenolic lignin structure s are degraded during the MnP-mediated peroxidation of unsaturated lip ids. (iii) In experiments crith MnP, Mn(II), and unsaturated lipid in vitro, this system mimicked intact C. subvermispora cultures in that i t cleaved nonphenolic beta-O-4 lignin model compounds between C-alpha and C-beta to release a benzylic fragment.