4-Ethylphenol metabolism by Aspergillus fumigatus.

Aspergillus fumigatus ATCC 28282 was found to be capable of growth on 4-ethylphenol as its sole carbon and energy source. A pathway for the metabolism of this compound has been proposed. The initial step involves hydroxylation of the methylene group of 4-ethylphenol to form 1-(4'-hydroxyphenyl)ethanol, followed by oxidation to 4-hydroxyacetophenone. The hydroxylase was NADPH and oxygen dependent, which is a characteristic of a monooxygenase type of enzyme. The 1-(4'-hydroxyphenyl)ethanol isolated from growth medium was a racemic mixture of R-(+) and S-(-) enantiomers. 4-Hydroxyacetophenone undergoes an NADPH-dependent Baeyer-Villiger type of oxygenation to give 4-hydroxyphenyl acetate, which is hydrolyzed to form hydroquinone (1,4-dihydroxybenzene). Hydroxylation of hydroquinone by an NADPH-dependent enzyme produces 1,2,4-trihydroxybenzene, the ring fission substrate, which is cleaved by ortho fission to form maleylacetate. The pathway was elucidated by various kinds of investigations. Analysis of culture medium sampled during growth on 4-ethylphenol revealed the transient appearance of 1-(4'-hydroxyphenyl)ethanol, 4-hydroxyacetophenone, and hydroquinone. Cells grown on 4-ethylphenol were able to oxidize all of these compounds immediately, whereas oxidation by succinate-grown cells showed a lag period. Extracts prepared from cells grown on 4-ethylphenol contained enzyme activities for all of the proposed steps. Apart from a low level of esterase activity towards 4-hydroxyphenyl acetate, extracts prepared from cells grown on succinate did not contain any of these enzyme activities.     

Bacterial metabolism of alpha-pinene: pathway from alpha-pinene oxide to acyclic metabolites in Nocardia sp. strain P18.3.

Over 20 gram-positive bacteria were isolated by elective culture with (+/-)-alpha-pinene as the sole carbon source. One of these strains, Nocardia sp. strain P18.3, was selected for detailed study. alpha-Pinene-grown cells oxidized, without lag, alpha-pinene, alpha-pinene oxide (epoxide), and the cis and trans isomers of 2-methyl-5-isopropylhexa-2,5-dienal. No other tested terpene was oxidized at a significant rate. alpha-Pinene was not metabolized by cell extracts in the presence or absence of NADH or NADPH. Cell extracts catalyzed a rapid decyclization of alpha-pinene oxide, in the absence of added cofactors, with the formation of cis-2-methyl-5-isopropylhexa-2,5-dienal. Further oxidation of the aldehyde to the corresponding acid occurred in the presence of NAD. Both activities were induced by growth with alpha-pinene. A rapid, nonenzymic transformation of the cis aldehyde into the trans isomer occurred in glycine buffer. The trans isomer was also a substrate for the NAD-linked aldehyde dehydrogenase. The distribution of the alpha-pinene oxide lyase in alpha-pinene-utilizing Pseudomonas spp. was also investigated and was compatible with the two alternative ring-cleavage sequences that have been proposed on the basis of accumulated metabolites.     

Fitness effects of amino acid replacements in the beta-galactosidase of Escherichia coli

Two genetic procedures were used to obtain amino acid replacements in the lacZ-encoded beta-galactosidase in Escherichia coli. Amino acid replacements could be obtained without regard to their effects on lactase activity by selecting spontaneous mutations that relieved the strong polarity of six nonsense mutations. When streaked on MacConkey- lactose indicator plates, approximately 75% of these mutants gave strong red lactose-fermenting colonies, and 25% gave white nonfermenting colonies. Mutants from 11 other nonsense codons were isolated directly using MacConkey-lactose indicator plates, on which positive color indication requires only 0.5% of the wildtype lactase activity. Among the total of 17 codons, 25 variant beta-galactosidases were identified using electrophoresis and thermal denaturation studies. The fitness effects of these variant beta-galactosidases were determined using competition experiments conducted with lactose as the sole nutrient limiting the growth rate in chemostat cultures. Three of the replacements were deleterious, one was selectively advantageous, and the selective effects of the remaining 21 were undetectable under conditions in which the smallest detectable selection coefficient was approximately 0.4%/generation.      

Atropine metabolism by a Pseudimanas sp.: Diauxic growth and oxidation of the products from esterase-mediated cleavage

Abstract Pseudomonas AT3 was isolated by elective culture with atropine as sole carbon source. Growth on atropine involved cleavage of the ester bond and was diauxic, with tropic acid being used in the first phase of growth followed by growth on the accumulated tropine moiety. During growth in N-limited medium, tropic acid was still used preferentially, nitrogen was provided from the tropine and novel keto compounds accumulated in the media. An inducible atropine esterase was synthesized during growth on atropine and, to a lesser extent, during growth on tropic acid and tropine. Organisms harvested from either phase of diauxic growth were able to oxidise tropic acid atropine. The ability of Pseudomonas AT3 to oxidase tropine was evident only in the second phase of growth and the greater extent of atropine oxidation in this phase reflected the ability to oxidase both cyclic components.     

Dynamic compression counteracts IL-1β induced inducible nitric oxide synthase and cyclo-oxygenase-2 expression in chondrocyte/agarose constructs

Background  

Nitric oxide and prostaglandin E₂ (PGE₂play pivotal roles in both the pathogenesis of osteoarthritis and catabolic processes in articular cartilage. These mediators are influenced by both IL-1β and mechanical loading, and involve alterations in the inducible nitric oxide synthase (iNOS) and cyclo-oxygenase (COX)-2 enzymes. To identify the specific interactions that are activated by both types of stimuli, we examined the effects of dynamic compression on levels of expression of iNOS and COX-2 and involvement of the p38 mitogen-activated protein kinase (MAPK) pathway.