Abstract 150

150. Li L., and R. M. Brown, Jr. 1993. ß-glucan synthesis in the cotton fiber. II. Regulation and kinetic properties ofß-glucan synthases. Plant Physiol. 101: 1143-1148.

150. Abstract

The regulation and kinetic properties of cellulose synthase aswell as ß-1,3-glucan synthase have been studied. The cellulosewas detected using acetic/nitric acid insolubility as an indicator of cellulose (this product contained only ß-1,4-linked glucans; K. Okuda, Li, L., K. Kudlicka, S. Kuga, R.M. Brown, Jr. [1993]Plant Physiol 101: 1131-1142). These studies reveal that: (a)ß-1,3-glucan synthesis is enhanced up to 31-fold by cellobiose with a Ka of 1.16mM; (b) cellulose synthesis is increased 12-foldby a combination of cellobiose (Ka = 3.26 mM) and cyclic-3':5'-GMP (Ks = 100 M); (C) the common components in the reaction mixture required by both enzymes are cellobiose, calcium, and digitonin;(d) cellulose synthase has an essential requirement for magnesium (Ka = 0.89 mM); (e) cellulose synthase also requires a low concentration of calcium (Ka= 90 M); (f) the optimal pH for cellulose synthase(7.6-8.0) is slightly higher than that for ß-1,3-glucansynthase (7.2-7.6); (g) the Km for UCP-Glc for cotton (Gossypium hirsutum) cellulose synthase is 0.40 mM; (h) the Km for UDP-Glc for for ß-1,3-glucan synthase is 0.43 mM.

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