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Biomedical subjects

J Ebel

Publications and source records attributed to J Ebel.

At least 55 records · Page 3Linked to original sources
PubMed1976

Enzymic synthesis of lignin precursors. Purification and properties of a cinnamoyl-CoA: NADPH reductase from cell suspension cultures of soybean (Glycinemax).

A cinnamoyl-coenzyme A reductase catalyzing the NADPH-dependent reduction of substituted cinnamoyl-CoA thiol esters to the corresponding cinnamaldehydes was isolated from cell suspension cultures of soybean (Glycine max L. var. Mandarin). A 1660-fold purification of the enzyme was achieved by (NH4)2SO4 fractionation, chromatography on DEAE-cellulose, hydroxyapatite and Sephadex G-100 and affinity chromatography on 5'-AMP-Sepharose. The apparent molecular weight of the reductase was found to be about 38 000 on the basis of the elution volume from a Sephadex G-100 column. Maximum rate of reaction was observed between pH 6.0 and 6.2 in 0.1-0.2 M citrate buffer at 30 degrees C. The enzyme was markedly inhibited by thiol reagents. The reductase showed a high degree of specificity for cinnamoyl-CoA esters. Feruloyl-CoA was the substrate with the lowest Km value (73 muM) and highest V (230 nkat/mg) followed by 5-hydroxy-feruloyl-CoA, sinapoyl-CoA, p-coumaroyl-CoA, caffeoyl-CoA and cinnamoyl-CoA. No reaction took place with acetyl-CoA. The Km value for NADPH varied with the type of substrate. Km values of 28, 120, and 290 muM were found with feruloyl-CoA, sinapoyl-CoA, and p-coumaroyl-CoA, respectively. The rate of reaction observed with NADH was only about 5% of that found with NADPH. The reaction products CoASH and NADP+ inhibited the reaction. The Ki values were in the range of 0.5-1 mM and the inhibition was of a noncompetitive (mixed) type. The role of the reductase in the biosynthesis of lignin precursors is discussed.

Aldehyde Oxidoreductases↗
PubMed1976

Host-Pathogen Interactions: IX. Quantitative Assays of Elicitor Activity and Characterization of the Elicitor Present in the Extracellular Medium of Cultures of Phytophthora megasperma var. sojae.

Resistance of soybean (Glycine max L.) seedlings to Phytophthora megasperma var. sojae (Pms) is in part due to the accumulation in infected tissue of a compound which is toxic to Pms. The accumulation of this compound, a phytoalexin called glyceollin, is triggered by infection, but it can also be triggered by molecules, "elicitors," present in cultures of Pms. The ability of the Pms elicitor to stimulate phytoalexin accumulation in soybean tissues has been used as the basis for biological assays of elicitor activity. Two bioassays were developed and characterized in this study of the Pms elicitor. These bioassays use the cotyledons and the hypocotyls of soybean seedlings. The cotyledon assay was used to characterize the extracellular Pms elicitor. This elicitor was isolated from Pms cultures and purified by ion exchange and molecular sieving chromatography. The extracellular Pms elicitor was determined to be a predominantly 3-linked glucan, which is similar in composition and structure to a polysaccharide component of Pms mycelial walls.

Journal Article↗
PubMed1976

Host-Pathogen Interactions: X. Fractionation and Biological Activity of an Elicitor Isolated from the Mycelial Walls of Phytophthora megasperma var. sojae.

An elicitor of phytoalexin production in soybean (Glycine max L.) tissues was isolated from purified Phytophthora megasperma var. sojae mycelial walls by a heat treatment similar to that used to solubilize the surface antigens from the cell walls of Saccharomyces cerevisiae. The wall-released elicitor is a discrete, minor portion of the P. megasperma var. sojae mycelial walls. The elicitor released from the mycelial walls was divided by diethylaminoethylcellulose and concanavalin A-Sepharose chromatography into four fractions, each having different chemical characteristics. The four fractions were obtained from each of the three races of P. megasperma var. sojae. The corresponding fractions from each of the three races are very similar in composition and elicitor activity. The results suggest that the elicitor activity of each fraction resides in the glucan component of the fraction. Evidence is presented to demonstrate that the elicitors are not race-specific and that the accumulation of glyceollin is not sufficient to account for race-specific resistance.

Journal Article↗
PubMed1976

Host-Pathogen Interactions: XI. Composition and Structure of Wall-released Elicitor Fractions.

The structures of the four wall-released elicitor fractions isolated from the Phytophthora megasperma var. sojae mycelial walls have been examined. The results demonstrate that fraction I is primarily composed of a branched beta-1,3-glucan, similar in structure to the extracellular elicitors described previously (Ayers, A., J. Ebel, F. Finelli, N. Burger, and P. Albersheim. 1976. Plant Physiol. 57: 751-759). Fractions II and IV are primarily composed of a highly branched mannan-containing glycoprotein, with fraction IV richer in protein than fraction II. Fraction III contains, attached to protein, a mixture of the two polysaccharide types found in fraction I and in fractions II and IV. The structural data presented here, in concert with the biological data presented in the previous two papers (Ayers et al. 1976. Plant Physiol. 57: 751-759; 760-765), demonstrate that the only compound produced by P. megasperma var. sojae which contains elicitor activity is the glucan. Evidence is presented that the terminal glycosyl residues of the glucan are required for elicitor activity. In addition, it is demonstrated that 90% of the glucan can be removed enzymically without any loss of biological activity. The active residue of the enzymic digestion is a highly branched 3- and 3,6-linked glucan containing about 4% mannosyl residues. The results presented suggest that the mannosyl residues of the glucan, which represent only about 1% of the undegraded glucan, are likely to participate in the active site of this molecule. The role of elicitors and phytoalexins in host-pathogen interactions is discussed. Evidence for the existence of and possible identity of another factor, which determines race specificity of host-pathogen interactions, is summarized.

Journal Article↗
PubMed1976

Host-Pathogen Interactions: XII. Response of Suspension-cultured Soybean Cells to the Elicitor Isolated from Phytophthora megasperma var. sojae, a Fungal Pathogen of Soybeans.

The glucan elicitor isolated from the mycelial walls of Phytophthora megasperma var. sojae, the fungus which causes stem and root rot in soybeans, stimulates the activity of phenylalanine ammonia-lyase and the accumulation of glyceollin in suspension-cultured soybean cells. Nigeran, a commercially available fungal wall glucan, was the only other compound tested which has any activity in this system. Glyceollin is a phenylpropanoid-derived phytoalexin which is toxic to P. megasperma var. sojae. Evidence is presented to support the hypothesis that the action of elicitors in stimulating phytoalexin synthesis is not species or variety specific but, rather, is part of a general defensive response of plants.

Journal Article↗
PubMed1975

Modification of phenylalanyl-tRNA synthetase from baker's yeast by proteolytic cleavage and properties of the trypsin-modified enzyme.

Earlier studies have shown that native phenylalanyl-tRNA synthetase from baker's yeast contains two different kinds of subunits, alpha of molecular weight 73000 and beta of molecular weight 63000. The enzyme is an asymmetric tetramer alpha-2beta-2, which binds two moles of each ligand per mole. Incubation of the purified enzyme with trypsin results in an irreversible conversion: the alpha-subunit remains apparently unchanged but beta is rapidly degraded and yields a lighter species beta of molecular weight 41000. The trypsin-modified enzyme is an alpha-2beta-2 molecule which can still activate phenylalanine but cannot transfer it to tRNA-Phe; furthermore it does not bind tRNA-Phe but its kinetic parameters are identical to those of the native enzyme with respect to ATP and phenylalanine. Therefore the two beta subunits play a critical part in tRNA binding. Isolated alpha or beta subunits exhibit no significant activity and both types of subunit seem to be required for phenylalanine activation.

Adenosine Triphosphate↗