The role of component C1 in cellulolytic systems

Abstract

out and the enzyme shows properties similar to that already obtained from several other plant tissues (McCrae, 1971), suggesting that the two pathways for malate oxidation may be a general property of higher-plant mitochondria. The operation of these two pathways may be of importance in controlling the redox equilibrium of NAD in the mitochondrial matrix and in the cytosol. Over the years, biological attack on cellulose has been variously attributed to a single enzyme, CMcellulase (Whitaker, 1953), or to a prime component called Cl thought to produce shorter chains for a more conventional hydrolysis by CM-cellulase (Reese et al., 1950). Other workers support a modified version of the last scheme in which the combined action of both CM-cellulase and component C1 is believed to be essential, since no specific function has so far been assigned to component C1 (Selby, 1968).Recent evidence from this laboratory showed that component C1 hydrolysed native cellulose to cellobiose in a solubilizing reaction promoted more effectively by cellobiase than by CM-cellulase (Halliwell & Riaz, 1971). Later preparations of component C1 indicate that the stimulation of cellulolysis so achieved can be increased even further by up to 80%. Prolonging the incubation beyond the usual period of 7 days had little effect on cellulolysis by component C1 alone. The additional presence of cellobiase, however, proved beneficial in enabling up to 70% solubilization of cotton to be attained in 21 days. The only products recognized chromatographically in the two systems were cellobiose and glucose respectively. The ability of cellobiase, which itself had no action on cellulose, to promote saccharification of the substrate by component C1 suggested that this component was inhibited by its product cellobiose. Inhibition was competitive, being dependent on the relative concentrations of cellulose and cellobiose and overcome completely by increasing the substrate concentration. CM-cellulose behaved similarly. Component C1 exhibits maximum activity and stability at pH5 and 37°C with Km approx. 0.05mg/ml. With cellulose and its derivatives component C1 apparently acts as a cellobiohydrolase with a preference for the ends of chains and in the vicinity of terminal non-reducing groups.

Fungal Cellulases

“…One proposal during this time was that C 1 was a protein that decrystallized cellulose by displacing native hydrogen bonds in the microfibril, leading to a more available structure for Cx . In 1969, Eriksson is credited with first proposing that an exoglucanase could be playing the role of C 1 , a view supported three years later in a report by Halliwell and co-workers . The landmark work reported by Berghem and Pettersson in 1973 clearly showed that an exo-cellulase, purified from T. viride , was highly active on crystalline cellulose and the best candidate for C 1 .…”

Carboxymethylcellulase Produced by Facultative Bacteria from the Hind-gut of the Termite Reticulitermes hesperus

“…Cellobiose is a competitive inhibitor of the cellulase activity of Trichoderma (Halliwell, Griffin & Vincent, 1972). The unexpected increase in CMC depolymerization rates in the presence of glucose or cellobiose made it imperative to assay the effects of adding carbohydrates under conditions where growth effects could be separated from enzymic activity.…”

Bacteriophage S6 requires bacterial cellulose for Erwinia amylovora infection

“…The C‐terminal part of Gp94 contains a glycosyl hydrolase (family 48) domain. Members of this family are endo‐ or exoglucanases that cleave cellulose (Myers and Northcote, 1959; Datta et al ., 1963; Halliwell et al ., 1972; Berghem and Pettersson, 1973; Eriksson and Pettersson, 1975).…”