Molecular recognition in the binding of vitamin B12 by the cobalamin-specific Intrinsic Factor

Equilibrium constants (given as log K/M-1) have been determined at pH 7.4 and 4 degrees C for binding by porcine Intrinsic Factor (B12-binding protein from the gut, specific for the 'cobalamin' series of Co corrinoids) of vitamin B12 or cyanocobalamin (10.5), cyanocobinamide, alpha-ribazole and alpha-ribazole-phosphate (main fragments produced by cleaving off the 'cobalamin' side-chain, all less than or equal to 3), and cyanocobinamide in the presence of greater than or equal to 10(-9) M ribazole (5.6 and independent of ribazole concentration), i.e. ribazole catalyses the binding of the cobinamide. It is proposed that the specificity of Intrinsic Factor for the cobalamins depends on the presence of the ribazole fragment in the cobalamin side-chain to promote an essential change in conformation before the corrinoid fragment can be bound.     

Fecapentaene concentration and mutagenicity in 718 North American stool samples

The fecapentaenes (FP) are the predominant fecal mutagens identified to date, but they have not been shown to be carcinogenic. Epidemiologists looking for other fecal mutagens that may be related to colorectal cancer must disentangle from their investigations the pervasive mutagenic effect of the fecapentaenes. As a first step to studying the epidemiology of fecal mutagenicity independent of fecapentaenes, we compared FP measurements and Salmonella mutagenicity assay results for 718 acetone-extracted stool samples collected from a variety of subjects in the Washington DC metropolitan areas. In this large group, 50% of mutagenic samples contained elevated fecapentaenes. Specifically, three-quarters of the samples mutagenic in TA100 contained high FP levels. In contrast, mutagenicity in TA98 was not generally explainable by fecapentaenes, suggesting that non-fecapentaene TA98 mutagenicity should be one focus of future efforts to uncover colorectal carcinogens of etiologic importance.     

Xylose dehydrogenase-1, a new gene on mouse chromosome 7

We report a new enzyme xylose dehydrogenase, the structural locus for which is on chromosome 7 of the mouse, closely linked to Tam-1. Three alleles have been detected in both laboratory strains and wild populations. Two of these determine proteins differing in electrophoretic mobility and the third is a null. This easily scored variation may prove useful both for gene mapping and in population genetics.This work was supported by the Medical Research Council.     

Biochemical characterization of canavalin, the major storage protein of jack bean

The structure of canavalin, a jack bean (Canavalis ensiformis) protein homologous to phaseolin, the major seed storage protein of Phaseolus vulgaris, has been investigated by x-ray crystallography and found to be a hexamer composed of three identical pairs of similar but nonidentical subunits related by a perfect 3-fold axis and pseudo dyad axes (strict C₃ and pseudo D₃). One member of each pair of subunits is derived from the amino terminal half of a precursor polypeptide of molecular weight 49,000 and the other from its carboxy terminal half. Thus, the crystallographic evidence indicates that the precursor polypeptide is a tandem duplicate and is structurally redundant (McPherson A. 1982 J Biol Chem 255: 10472). A number of physical and chemical properties of the protein in both the uncleaved and the cleaved form were investigated. These included the native molecular weights, amino acid analyses, number of exposed sulfhydryl groups, carbohydrate content, metal ion analysis, crystallization behavior, and the fate of the protein in developing seeds. It was also found that the purified precursor protein possesses a substantial level of α-d-mannosidase activity and seems to share a number of other physical and chemical properties with that enzyme.     

Niche changes between parasite populations: An example from ticks on reptiles

Summary Two Australian tick species Aponomma hydrosauri and Amblyomma albolimbatum have the same major host species, the lizard Trachydosaurus rugosus. While females of Amb. albolimbatum are most often attached in the ears and on the neck of their hosts, Ap. hydrosauri females prefer to attach further back, under the forearms and on the back. Males show the same interspecific difference but there is also a difference between populations. Ap. hydrosauri males from populations in contact with Amb. albolimbatum attach more often in posterior positions than Ap. hydrosauri males from populations isolated from Amb. albolimbatum. These differences were found in both field populations and laboratory reared ticks. Phylogenetic evidence suggests that the change in male attachment site between Ap. hydrosauri populations followed the colonization of T. rugosus. We propose that the most likely reason for the change of attachment sites has been interspecific interactions with Amb. albolimbatum and that competition has been for space for efficient reception of female signals.     

Genetic regulation of alcohol dehydrogenase C2 in the mouse. Developmental consequences of the temporal locus (Adh-3t) and positioning of Adh-3 on chromosome 3

The tissue specificity of a proposed cis-acting temporal locus (Adh-3t), which regulates alcohol dehydrogenase C₂ (ADH-C₂) activity in mouse reproductive tissue extracts, has been examined in C5 7BL/6J, SM/J, F₁ (SM/J × C5 7BL/6J) mice as well as in progeny of an (F₁ [SM/J × C5 7BL/6J] × C5 7BL/6J) back-cross. Electrophoretic variants for ADH-C₂, previously used to localize the gene (Adh-3) encoding this enzyme on chromosome 3, enabled the relative parental contributions to ADH-C₂ phenotype in F¹ and backcross mouse tissues to be determined. These analyses demonstrated that (1) stomach, kidney, lung, adrenals, seminal vesicles, epididymis, uterus, and ovary ADH-C₂ is encoded by a single locus (Adh-3); Adh-3t is differentially active in various tissues, eg, lung exhibits no apparent activity whereas the temporal locus is fully active in seminal vesicles; (3) Adh-3t is probably differentically active in different cells of some tissues, eg, adrenals. Specific activity profiles of stomach and epididymal ADH-C₂ during the neonatal development of C5 7BL/6J, SM/J, and F₁ (SM/J × C5 7BL/6J) male mice supported the proposal for a cis-acting temporal locus for this enzyme. Genetic analyses examining segregation of Adh-3 and Adh-3t among backcross progeny suggested that these are distinct but closely linked loci, since one recombinant among 256 progeny was observed. Linkage data of Adh-3 with Va (varitint-waddler) and de (droopy ear) was also obtained, which suggested that Adh-3 is localized on chromosome 3 between Va and de.     

Mutagenicity of trialkyltriazenes: Mutagenic potency of alkyldiazonium ions,the putative ultimate carcinogens from dialkylnitrosamines

Although aryldialkyltriazenes have been known for many years and their mutagenic, carcinogenic and carcinostatic properties have been investigated, almost nothing is known of the related trialkyltriazenes. Our recently developed general preparative route to these substances has allowed the examination of the mutagenic properties of several representative examples of this class of compounds. This, 1-benzyl-3,3-dimethyl-, 3-benzyl-1,3-dimethyl-, 3-benzyl-3-ethyl-1-n-butyl- and 1,3-di-n-butyl-3-methyltriazenes are direct acting mutagens in the TA1535 strain of Salmonella typhimurium. The respective mutagenic potencies of these substances can be accounted for by the in situ generation of alkyldiazonium ions. These ions are considered to be strong candidates for the ultimate mutagens/carcinogens derived from some dialkylnitrosamines.     

An investigation of the location and possible compartmentation of the precursor pool of phenylalanine for protein synthesis in human granulocytes.

Evidence is presented that in human granulocytes the immediate precursor pool of phenylalanine for protein synthesis in vitro is intracellular significant compartmentation.