Lignin Peroxidase Isozymes from Phanerochaete chrysosporium Can Be Enzymatically Dephosphorylated

Abstract

The extracellular lignin peroxidase (LIP) protein profile of the fungus Phanerochaete chrysosporium, grown in nonimmersed liquid culture under conditions of excess nitrogen, changed markedly with culture age. At peak LIP activity (day 4), the heme-protein profile in the extracellular fluid, analyzed by anion-exchange high-pressure liquid chromatography, was characterized by a predominance of the LIP isozymes H1 and H2, small amounts of H6 and H8, and other minor peaks, designated Ha and Hb. On day 5, the level of H1 increased and it became the dominant isozyme, with a corresponding decrease in the level of H2. Moreover, the relative levels of H6 and H8 decreased with corresponding increases in Ha and Hb levels. This change in LIP profile occurred extracellularly and resulted from the enzymatic dephosphorylation of LIP isozymes. An enzymatic fraction responsible for LIP isozyme dephosphorylation, termed LIP dephosphorylating (LpD) fraction, was partially purified from the culture fluid. Incubation of the LpD fraction with (sup32)P-labeled H2, H6, H8, and H10 isozymes separated from nitrogen-limited cultures resulted in the formation of the dephosphorylated isozymes H1, Ha, Hb, and Hc, respectively. Dephosphorylation did not significantly change the catalytic properties of the LIP isozymes with veratryl alcohol as a substrate. LIP dephosphorylation is therefore suggested to be a posttranslational modification process catalyzed extracellularly by the LpD activity.