PubMed · 1395608
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J E Wahlberg. 1992. Hardening.. https://doi.org/10.1111/j.1600-0536.1992.tb00140.x
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Ferric soybean lipoxygenase forms stable complexes with 4-substituted catechols. The structure of the complex between the enzyme and 3,4-dihydroxybenzonitrile has been studied by resonance Raman, electron paramagnetic resonance, visible, and X-ray spectroscopies. It is a bidentate iron-catecholate complex with at least one water ligand. The kinetics of formation of complexes between lipoxygenase and 3,4-dihydroxybenzonitrile and 3,4-dihydroxyacetophenone have been studied by stopped-flow spectroscopy. The data are consistent with two kinetically distinct, reversible steps. The pH dependence of the first step suggests that the substrate for the reaction is the catechol monoanion. When these results are combined, plausible mechanisms for the complexation reaction are suggested.
We recently reported that tyrphostin 23 (3,4-dihydroxybenzylidene malononitrile) is unstable in solution and that some of the degradation products are better inhibitors of the tyrosine kinase activity of Src and the EGF-receptor kinase than the parent compound itself (Ramdas et al., Cancer Res. 54, 867-868, 1994). In this study, the tyrphostin 23-derived compound designated P3, which is a more stable and potent protein tyrosine kinase inhibitor, was isolated. P3 was purified from oxidized tyrphostin 23 by solvent extraction, silica-gel flash chromatography, and reverse-phase high-pressure liquid chromatography. The physical characteristics of the isolated compound were determined and its chemical structure elucidated by 1H and 13C NMR spectroscopy. The proposed structure of this new inhibitor is that of a tyrphostin 23 dimer joined at the benzylidene carbon. P3 was evaluated in vitro as an inhibitor of four different protein tyrosine kinases (Src, Csk, EGF-receptor, and FGF-receptor) and two protein serine kinases (PK-A and PK-C). This compound exhibited the most inhibitory activity against Src with a Ki value of 6 microM and was less inhibitory toward the other protein kinases with Ki values ranging from 35 to 300 microM. P3 did not inhibit other nucleotide-utilizing enzymes such as lactate dehydrogenase and hexokinase. The growth and colony formation of HT-29 colon adenocarcinoma cells that contain activated Src was inhibited by P3 with an IC50 value of approximately 10 microM.
Transgenic tobacco plants that express the bacterial nahG gene encoding salicylate hydroxylase have been shown to accumulate very little salicylic acid and to be defective in their ability to induce systemic acquired resistance (SAR). In recent experiments using transgenic NahG tobacco and Arabidopsis plants, we have also demonstrated that salicylic acid plays a central role in both disease susceptibility and genetic resistance. In this paper, we further characterize tobacco plants that express the salicylate hydroxylase enzyme. We show that tobacco mosaic virus (TMV) inoculation of NahG tobacco leaves induces the accumulation of the nahG mRNA in the pathogen infected leaves, presumably due to enhanced stabilization of the bacterial mRNA. SAR-associated genes are expressed in the TMV-infected leaves, but this is localized to the area surrounding necrotic lesions. Localized acquired resistance (LAR) is not induced in the TMV-inoculated NahG plants suggesting that LAR, like SAR, is dependent on SA accumulation. When SA is applied to nahG-expressing leave's SAR gene expression does not result. We have confirmed earlier reports that the salicylate hydroxylase enzyme has a narrow substrate specificity and we find that catechol, the breakdown product of salicylic acid, neither induces acquired resistance nor prevents the SA-dependent induction of the SAR genes.