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Biomedical subjects

H Grisebach

Publications and source records attributed to H Grisebach.

At least 55 records · Page 3Linked to original sources
PubMed1975

Purification and properties of isoenzymes of cinnamyl-alcohol dehydrogenase from soybean-cell-suspension cultures.

Two isoenzymes of an NADP+ -dependent cinnamyl alcohol dehydrogenase and an NAD+ - dependent aliphatic alcohol dehydrogenase were extracted from cell suspension cultures of soybean (Glycine max L., var. Mandarin) which form lignin during growth. These enzymes could be separated from each other by chromatography on DEAE-cellulose and hydroxyapatite. The cinnamyl alcohol dehydrogenase isoenzymes were partially purified by (NH4)2SO4 fractionation, and column chromatography on DEAE-cellulose, Sephadex G-100, and hydroxyapatite. The molecular weight of the enzymes were estimated by the elution volumes from a Sephadex G-100 column and were found to be about 43,000 (isoenzyme 1) and 69,000 (isoenzyme 2). Maximum rates of reaction were observed in the case of coniferyl alcohol oxidation at pH 9.2 (Isoenzyme 1) and pH 8.8 (isoenzyme 2); in the reverse reaction pH 6.5 was optimal for isoenzyme 2. Whereas isoenzyme 1 is specific for coniferyl alcohol, isoenzyme 2 can also oxidize cinnamyl alcohol and a number of substituted cinnamyl alcohols, Km values for substituted cinnamaldehydes are 3-11 times lower than for the corresponding alcohols. Neither isoenzyme reacted with benzyl alcohol, anisic alcohol or ethanol. Substrate inhibition for the forward and reverse reaction was found with isoenzyme 2 but not with isoenzyme 1. The equilibrium constant was determined to be about 10(9) in favour of coniferaldehyde reduction. The possible role of the cinnamyl alcohol dehydrogenase in lignin biosynthesis is discussed.

Alcohol Oxidoreductases↗
PubMed1975

Spectroscopic evidence for the formation of a 4-keto intermediate in the UDP-apiose/UDP-xylose synthase reaction.

Uridine diphospho-D-glucose (UDP-Glc) and UDP-methyl-D-glucuronate (UDP-GlcUAMe) have been shown to be competitive inhibitors for the UDP-apiose/udp-xylose synthase from cell suspension cultures of parsley. The apparent Ki values for these substrate analogues were of the same order of magnitude as the apparent Km value for the substrate UDP-D-glucuronic acid (UDP-GlcUA). The difference spectrum of the incubation mixture containing UDP-GlcUA, NAD+ and the highly purified enzyme showed a transient absorption with a maximum at 292 nm which disappeared upon addition of sodium hydroxide. The incubation with UDP-Glc or UDP-GlcUAMe also showed and NAD+-dependent absorption at 292 nm. However, in these cases a strong enhancement of the absorption at alkaline pH and a shift of the absorption maximum to longer wavelength were observed. Upon addition of 0-phenylenediamine to the enzyme incubation with UDP-Glc or UDP-GlcUAe a strong absorption with a maximum at respectively 335 and 315 nm appeared. The results show the transient formation of a 4-keto derivatives in the synthase reaction with the normal substrate UDP-GlcUA. The substrate analogues UDP-Glc and UDP-GlcUAMe can also be oxidized at C-4 by the enzyme in the presence of NAD+ to stable 4-keto derivatives which give rise to a strong absorption at alkaline pH or after reaction with o-phenylenediamine.

Binding Sites↗