FIG. 1.

Purification of DRMs by flotation in sucrose gradient. After solubilization of plasma membranes by Triton X-100, the insoluble material was layered under a linear 20 to 40% sucrose gradient and ultracentrifuged (see Materials and Methods). Two peaks of protein were observed, one corresponding to DRMs (fractions 5 to 8) and the other corresponding to a pellet containing high-density structures not solubilized by Triton X-100 (fraction “0”). Chitin and (1→3)-β-d-glucan synthase activities were assayed in each fraction of the gradient. They are expressed as nmol of GlcNAc incorporated into chitin per ml of fraction in 1 h and as μmol of Glc incorporated into (1→3)-β-d-glucan per ml of fraction in 1 h, respectively.