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The 2-(2,4-dichlorphenoxy)propionic acid (2,4-DP)-degrading bacterial strain MH was isolated after numerous subcultivations of a mixed culture obtained by soil-column enrichment and finally identified as Flavobacterium sp. Growth of this strain was supported by 2,4-DP (maximum specific growth rate 0.2 h-1) as well as by 2,4-dichlorophenoxyacetic acid (2,4-D), 4-(2,4-dichlorophenoxy)butyric acid (2,4-DB), and 2-(4-chloro-2-methylphenoxy)propionic acid (MCPP) as sole sources of carbon and energy under aerobic conditions. 2,4-DP-Grown cells (10(8] of strain MH degraded 2,4-dichlorophenoxyalkanoic acids, 2,4-dichlorophenol (2,4-DCP), and 4-chlorophenol at rates in the range of 30 nmol/h. Preliminary investigations indicate that cleavage of 2,4-DP results in 2,4-DCP, which is further mineralized via ortho-hydroxylation and ortho-cleavage of the resulting 3,5-dichlorocatechol.

High pressure liquid chromatography has been used to study the acid soluble nucleotide pool of Saccharomyces cerevisiae under different conditions of growth. ATP, ADP, AMP, NAD, GTP, UTP, UDP, CTP, CDP, and UDP-sugars plus UMP could be separated and were found in concentrations higher than 0.1 mumol per g yeast cell dry weight (= detection limit). During glucose-limited continuous culture the levels of individual nucleotides depended on the growth rate, which was most pronounced with pyrimidine (uridine, cytidine) nucleotides. The energy charge (E.C.) remained high (0.9) at all growth rates (0.07-0.3 h-1). During synchronized growth at a constant growth rate (0.11 h-1) almost all nucleotide levels and the E.C. remained at constant values with the only exception of UDP-sugars and UMP of which increased levels were found during the phase of budding. Under conditions of metabolic stress (addition of antimycin A, deoxyglucose plus iodoacetate) pronounced changes in the levels of purine (adenine and guanine) nucleotides and the E.C. were observed. All other nucleotides were less influenced by these conditions. Only under these conditions IMP accumulation was observed. The results strongly argue against the significance of purine nucleotide or E.C. measurements under viable conditions. In contrast, changes in the levels of pyrimidine nucleotides seem to be indicative of changes in the flux through the metabolic pathways where they act as coenzymes.

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Xylose reductase (xylitol: NADP oxidoreductase, EC 1.1.1.139) has been purified from D-xylose grown cells of the yeast Pachysolen tannophilus by application of DEAE-cellulose ion exchange chromatography, 2′,5′-ADP-Sepharose affinity chromatography, Biogel P200 gel filtration, and dextran blue Sepharose chromatography to approximately 95% homogeneity. It consists of a single polypeptide chain with a relative molecular weight of 35 000–40 000 and an isoelectric point of pH 4.9. The enzyme has a broad substrate specificity similar to that of aldose (or aldehyde) reductases from mammalian tissues. It exhibits Michaelis–Menten type kinetics (Km D-xylose, 162 mM; Km D-xylitol, 212 mM; Km NADPH, 0.059 mM; [Formula: see text], 0.071 mM). The enzyme is specific for NADPH; activity with NADH is below 0.5% of Vmax observed with NADPH. The reduction of xylose is inhibited by NADP, the anabolic reduction charge (NADPH/NADP + NADPH), and also in a complex manner by ATP. At physiological pH values the equilibrium is Keq = 10−10. The importance of these findings for the physiology of xylose fermentation by this yeast is discussed.