The use of picolinyl esters for the characterization of microbial lipids: application to the unsaturated and cyclopropane fatty acids of campylobacter species

Picolinyl esters have been recently introduced for the mass spectrometric structure determination of unsaturated and cyclopropane fatty acids. We have used these derivatives to characterize the unsaturated and cyclopropane acids of Campylobacter species . The principle unsaturated acids were shown to be 11-octadecenoic acid, with smaller amounts of 9-hexadecenoic acid, 9-octadecenoic acid and 9, 11-octadecadienoic acid. The only cyclopropane acid present was cis 11, 12-methylene octadecanoic acid. There was no interspecific variation in the position of unsatu-ration or methylene bridges, even in the recently discovered gastric Campylobacter like organisms (GCLO) or the urease positive thermophilic Campylobacters (UPTC), the fatty acid profiles of which were consistent with their inclusion in the genus Campylobacter .     

Biochemical pathways in prokaryotes can be traced backward through evolutionary time

For the first time, a credible prokaryotic phylogenetic tree is being assembled by Woese and others using quantitative sequence analysis of oligonucleotides in the highly conservative rRNA. This provides an evolutionary scale against which the evolutionary steps that led to the arrangement and regulation of contemporary biochemical pathways can be measured. This paper presents an emerging evolutionary picture of aromatic amino acid biosynthesis within a large superfamily assemblage of prokaryotes that is sufficiently developed to illustrate a new perspective that will be applicable to many other biochemical pathways.      

Chorismate mutase/prephenate dehydrogenase from Escherichia coli K12: purification, characterization, and identification of a reactive cysteine

The bifunctional enzyme involved in tyrosine biosynthesis, chorismate mutase/prephenate dehydrogenase, has been isolated from extracts of a regulatory mutant of Escherichia coli K12. The pure enzyme is a homodimer of total molecular weight 78 000 and displays Michaelis-Menten kinetics for both activities. Fingerprinting and amino acid sequencing of tryptic and thermolytic peptides of the S-[14C]carboxymethylated enzyme allowed the identification of three unique cysteine-containing sequences per subunit. Chemical modification of the native enzyme with 5,5'-dithiobis(2-nitrobenzoate) or iodoacetamide showed that one sulfhydryl group per subunit was particularly reactive, and the integrity of this group was essential for both enzymic activities. This work supports previous proposals for a close spatial relationship between the active sites.     

Induction of 7-ethoxycoumarin o-deethylase activity in cultured human epithelial cells by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD): evidence for TCDD receptor

The responsiveness of 5 human squamous cell carcinoma (SCC) lines derived from tumors of the epidermis and tongue to 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) was assessed by measuring the induction of the cytochrome P1-450-mediated monooxygenase activity, 7-ethoxycoumarin O-deethylase (ECOD). In 4 of the SCC lines the EC50 for this response was approximately 10(-9)M, whereas in one line the EC50 was 10(-10)M. In each of the less sensitive lines a concentration of 10(-10)M TCDD elicited less than 5% of the maximal enzyme activity. Specific binding of radiolabeled TCDD was detected in the cytosol fraction from all the SCC lines. The relative amount of receptor measured in each line correlated with maximally-induced ECOD activity. The data indicate that human cell lines derived from a target tissue for TCDD toxicity contain the TCDD receptor and show differential sensitivity to TCDD analogous to the murine strain differences in sensitivity regulated by the Ah locus.     

Properties of a neutral allele model with intragenic recombination

An infinite-site neutral allele model with crossing-over possible at any of an infinite number of sites is studied. A formula for the variance of the number of segregating sites in a sample of gametes is obtained. An approximate expression for the expected homozygosity is also derived. Simulation results are presented to indicate the accuracy of the approximations. The results concerning the number of segregating sites and the expected homozygosity indicate that a two-locus model and the infinite-site model behave similarly for 4Nu less than or equal to 2 and r less than or equal to 5u, where N is the population size, u is the neutral mutation rate, and r is the recombination rate. Simulations of a two-locus model and a four-locus model were also carried out to determine the effect of intragenic recombination on the homozygosity test of Watterson (Genetics 85, 789-814; 88, 405-417) and on the number of unique alleles in a sample. The results indicate that for 4Nu less than or equal to 2 and r less than or equal to 10u, the effect of recombination is quite small.