Accessibility of sulfite pulp to lignin peroxidase and marker proteins with respect to enzymatic bleaching

Abstract

The diffusion of proteins into unbleached and bleached sulfite pulp fibers was investigated. Pulp specimens were infiltrated with crude lignin peroxidase of Phanerochaete chrysosporium (40,000–46,000 Da), ovalbumin (43,000 Da) and myoglobin (16,500 Da), cross-linked by glutaraldehyde and processed for immunoelectron microscopy. Ultra-thin sections of the specimens were labeled for the proteins with antibodies conjugated to colloidal gold. The penetrability of the fibers was determined qualitatively by comparison of the gold-labeling density inside and outside the fibers. The results showed great differences with respect to the penetrability of individual fibers in one and the same pulp specimen, correlating with the morphological appearance of the fibers. A large part of the fibers is fully accessible to enzymatic attack, but many fibers are not. Enzyme-substrate interaction between lignin peroxidase and residual lignin was evident: contrary to the two inert proteins, a great enrichment of the fibers with the enzyme was observed with lignin peroxidase.