PubMed · 13606632
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F DE LILLO. [Serum procainesterase and hyperthyroidism].. https://pubmed.ncbi.nlm.nih.gov/13606632/
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Purified thiocarbamate-inducible ThcF of Rhodococcus erythropolis NI86/21, overexpressed in Escherichia coli, displayed several characteristics of the HASH family of enzymes that groups prokaryotic proteins of the alpha/beta hydrolase superfamily possessing serine-dependent hydrolase and/or haloperoxidase activity. Kinetic analysis of bromination and ester hydrolysis revealed a low affinity of ThcF for model substrates. Sulfoxidation of thiocarbamates was demonstrated but probably represents a side activity due to peroxoacid generation by the enzyme. The thcF-linked thcG gene, encoding a LAL-type regulator, triggers expression of thcF in Rhodococcus. The tandem gene organization thcG-thcF is conserved in the thiocarbamate-degrading strain Rhodococcus sp. B30. It is proposed that HASH enzymes may be involved in the metabolism of plant-derived compounds.
Salicylates are defensive compounds against a great variety of generalist herbivores. Salicortin and its derivatives are labile compounds that degrade immediately when cell compartmentalization is ruptured, producing a 6-hydroxy-2-cyclohexenone (6-HCH) moiety that is a strong antifeeding cue. We studied the in vitro degradation of willow salicylates in the presence and absence of foliar enzymes at acidic, neutral, and alkaline pHs. Higher substituted salicylates were degraded in the absence of foliar enzymes at alkaline pH and in the presence of foliar enzymes at all three pHs. Salicin and its diglucoside, on the other hand, were degraded only in the presence of foliar enzymes at acidic pH, probably by beta-glucosidase activity. The main degradation products of higher substituted salicylates were salicin, 6-HCH, and catechol in both the absence and presence of enzymes, suggesting that the production of 6-HCH and catechol do not necessarily demand enzymatic activity. We propose that the degradation of salicylates begins with the cleavage of a 1-hydroxy-6-oxo-2-cyclohexen-1-carbonyl moiety by foliar esterases and/or alkaline condition. This moiety is decarboxylated in nonenzymatic reaction to an anion of 2-hydroxy-3-cyclohexenone, which is tautomerized to the enol form and further to the keto form, 6-HCH. Hydroxyketone can be also oxidized to catechol, a substrate of polyphenol oxidases.
Design, synthesis, and esterase and ion channel activity of a novel barrel-stave supramolecule with hydrophobic exterior and histidine-rich interior are reported. Voltage-dependent binding of pyrenyl-8-oxy-1,3,6-trisulfonates by histidines within p-octiphenyl beta-barrels (and not monomers) via ionic (and not hydrophobic) interactions (K(D), K(I), K(M) < 1 microM) is the basis for superb esterolytic proficiency up to (k(cat)/K(M))/k(uncat) = 9.6 x 10(5) in water and bilayer membranes. The conductance of labile ion channels formed in planar bilayer membranes is shown to be reduced by 8-hydroxypyrene-1,3,6-trisulfonate on the single- and multichannel level. [reaction: see text]