Denaturation and Renaturation of a β-1,6;1,3-Glucan, Lentinan, Associated with Expression of T-Cell-mediated Responses

Correlation between the higher structure and biological functions of lentinan, a β-1,6;1,3-glucan capable of potentiating T- and non-T-cell-mediated responses, were investigated by measurements of optical rotation and some biological responses. The addition of urea or dimethyl sulfoxide decreased specific rotation at 589 nm, [α]_d, of lentinan in a concentration-dependent manner and the removal of these denaturants resulted in the recovery of [α]_d values. Measurements of optical rotatory dispersion in the spectral region between 600 and 200 nm showed the change in the higher structure of lentinan more clearly. Denaturation and renaturation of lentinan using urea and dimethyl sulfoxide were associated with the decrease and the recovery of antitumor activity against P-815 mastocytoma and vascular dilation and hemorrhage-inducing activity, found to be T-cell-mediated responses. Lentinan was also denatured by NaOH and the transition of [α]_d values and optical rotatory dispersion curves were seen in the manner of two concentration-dependent phases. Removal of NaOH led to the recovery of optical rotation of lentinan and its antitumor and vascular dilation and hemorrhage-inducing activity. However, recovery of these bioactivities was more difficult in the case of the higher concentrations of NaOH above 2% than the lower ones. During the process of renaturation of lentinan, random aggregation may take place. An increase of serum acute phase proteins, a non-T-cell-mediated response caused by lentinan, was not affected by the change of the higher structure of lentinan.