No abstract

No abstract

When [glucitol-3 H]XXFGol (a NaB 3 H 4 -reduced xyloglucan nonasaccharide) was applied to excised shoots of pea (Pisum sativum L. cv. Progress) at the base of the epicotyl, it inhibited growth in the elongation zone, 4±5 cm distal. Experiments were conducted to discover whether such 3 H-oligosaccharides are translocated intact over this distance, or whether an intercellular second messenger would have to be postulated. After 24 h, 3 H from [glucitol-3 H]XXFGol and [glucitol-3 H]XXXGol showed U-shaped distributions, with most 3 H at the base and apex of the stem. Radioactivity from [fucosyl-3 H]XXFG and [xylosyl-3 H]XXFG also moved acropetally, but did not concentrate at the apex, possibly owing to removal from the transpiration stream of fucose and xylose formed by partial hydrolysis of XXFG en route. When 10 A7 M [glucitol-3 H]XXFGol was supplied, about 14 fmol á seedling ±1 of apparently intact [ 3 H]XXFGol was extractable from the elongation zone after 24 h. Larger amounts of degradation products were extractable (including free [ 3 H]glucitol) and some wall-bound 3 H-hemicellulose was present (presumably formed by the oligosaccharides acting as acceptor substrates for transglycosylation). We conclude that biologically active oligosaccharides of xyloglucan can move through the stem acropetally and that they are maintained at low steady-state concentrations by both hydrolysis and transglycosylation.

A 3 β-hydroxysteroid oxidoreductase was isolated and characterized in the microsomes of Digitalis lanata cell cultures. The enzyme catalyzes the conversion of 5α-pregnane-3,20-dione to 5a-pregnan-3 β-ol-20-one and requires NAD(P)H2. The enzyme was found to have a pH optimum of 80. The reaction had an optimum incubation temperature of 25 °C with linear reduction for the first 4 h, reaching maximum enzyme activity after 7 h. Substrate kinetics for 5a-pregnane-3,20-dione and NADPH2 resulted in apparent Km-values of 18.5-20 (µM for 5a-pregnane-3,20-dione and 50-120 µM for the co-substrate NADPH2. In order to localize 3β-hydroxysteroid oxidoreductase differential centrifugation as well as linear sucrose density gradient centrifugation were performed. The results obtained lead to the conclusion that 3β-hydroxysteroid oxidoreductase is not associated with a single cell compartment, but consists of a major soluble part and a markedly smaller part of endoplasmic reticulum-associated activity

No abstract