Transmission electron microscopy was used to investigate the ultrastructural features of diverse cellulase and cellulase-xylanase multiprotein complexes that are components of the cellulase-xylanase system of Clostridium papyrosolvens C7. The multiprotein complexes were separated by anion-exchange chromatography into seven biochemically distinguishable fractions (F1 to F7). Most individual F fractions contained, in relatively large numbers, an ultrastructurally recognizable type of particle that occurred only in smaller numbers, or not at all, in the other F fractions. It is suggested that these ultrastructurally distinct particles represent the biochemically distinct multiprotein complexes that constitute the cellulase-xylanase system of C. papyrosolvens C7. Some of the particles consisted of tightly packed globular components that appeared to be arranged in the shape of a ring with conical structures pointing out along its axis. Other particles had triangular, polyhedral, or star shapes. The major protein fraction (F4) almost exclusively contained particles consisting of loosely aggregated components, many of which appeared to be arranged along filamentous structures. The ultrastructural observations reported here support our previous conclusion that the cellulase-xylanase system of C. papyrosolvens C7 comprises at least seven different high-molecular-weight multiprotein complexes. Furthermore, results of this and earlier studies indicate that the interactions between C. papyrosolvens C7 and cellulose are different from those that have been described for Clostridium thermocellum.
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