MANNITOL BIOSYNTHESIS IN PYRENOCHAETA TERRESTRIS .I. D-MANNITOL-1-PHOSPHATE - NAD OXIDOREDUCTASE

Cell‐free extracts of mycelial mats of Pgrenochaeta terrestris grown in stationary culture on synthetic glucose or sucrose ‐ salts liquid media contained D‐mannitol‐1‐Phosphate:NAD oxidoreductase (EC 1.1.1.17) activity. Greatest activity occurred early in the growth period. The optimum pH for the reduction of NAD+ in the presence of Fru‐6‐P was 7.4–7.5 while the optimum pH for the oxidation of NADH in the presence of Mtl‐1‐P was 8.1–8.2. The enzyme was stabilized to some extent in Tris‐maleate buffer, pH 7.5, and by the addition of 10% (NH4)2SO4, to this buffer. A 10‐ to 16‐fold purification was attained by a combination of (NH4)2SO4 fractionation and gel filtration on Sephadex G‐100. The enzyme was relatively specific in its substrate and coenzyme requirements. The Km values were determined as: Fru‐6‐P ‐ 3 × 10−4 M, Mtl‐1‐P ‐ 1 × 10−4 M, and NAD+ and NADH ‐ 3 × 10−5 M. Copyright © 1969, Wiley Blackwell. All rights reserved