beta-Glucoside Activators of Mung Bean UDP-Glucose: beta-Glucan Synthase : II. Comparison of Effects of an Endogenous beta-Linked Glucolipid with Synthetic n-Alkyl beta-d-Monoglucopyranosides.

n-Alkyl (C(6)-C(12)) beta-d-monoglucopyranosides have been found to be highly potent activators of mung bean beta-glucan synthase in vitro, increasing the V(max) of the enzyme as much as 60-fold and with K(a) values as low as 10 micromolar. Activation is highly specific for the beta-linked terminal glucose residue; other alkyl glycosides such as, octyl-alpha-glucoside, dodecyl beta-maltoside, 6-lauryl sucrose, 6-lauryl glucose, which lack this structure, are ineffective as activators. Based on the similarities in their structure and effects on beta-glucan synthesis under a variety of conditions, it is proposed that the alkyl beta-glucosides are structural analogs of the native glucolipid activator of beta-glucan synthase isolated from mung bean extracts.

beta-Glucoside Activators of Mung Bean UDP-Glucose: beta-Glucan Synthase : I. Identification of an Endogenous beta-Linked Glucolipid Activator.

Heat-stable activators of membranous beta-glucan synthase have been isolated from the supernatant fraction of crude mung bean (Vigna radiata) extracts by DEAE-cellulose and silica-gel chromatography. One of the activators has been partially purified and characterized on the basis of susceptibility to various enzymes and by analysis of the products formed upon total acid hydrolysis, alkaline-methanolysis, and beta-glucosidase digestion. This activator has the characteristics of a 1,2-dioleoyl diglyceride containing beta-linked glucose residue(s) at the C-3 position.

Regulation of cellulose synthesis in Acetobacter xylinum by cyclic diguanylic acid.

Cellulose is the most abundant renewable carbon resource on earth and is an indispensable raw material for the wood, paper, and textile industries. A model system to study the mechanism of cellulose biogenesis is the bacterium Acetobacter xylinum which produces pure cellulose as an extracellular product. It was from this organism that in vitro preparations which possessed high levels of cellulose synthase activity were first obtained in both membranous and soluble forms.

An unusual guanyl oligonucleotide regulates cellulose synthesis in Acetobacter xylinum.

The mechanism of GTP-specific activation of the membrane-bound cellulose synthase system of Acetobacter xylinum has been further elucidated. The supernatant fraction derived from washed membranes of this organism contains an enzyme which reacts with GTP to form a low molecular mass, heat-stable compound,tentatively characterized as a cyclic oligonuleotide composed of GMP residues, which is the immediate activator of the cellulose synthase. This activation is reversed by a membrane-bound enzyme that degrades the activator; the latter enzyme is inhibited by Ca (2+).

Cyclic nucleotide phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, induces cytodifferentiation of follicular granulosa cells cultured in serum-free medium.

Cultured granulosa cells from intact immature rats produced large amounts of progestins in response to phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (MIX). MIX alone stimulated up to 9 times higher amounts of 20 alpha-hydroxy-4-pregnen-3-one (20 alpha-OH-P) when compared with FSH (100 ng/ml)-stimulated steroidogenesis. Combined action of MIX and FSH did not yield more activity than MIX action alone.