The deviation from linkage equilibrium with multiple loci varying in a stepping-stone cline

The balance between the creation of associations between alleles at different loci by immigration and the convergence to linkage equilibrium due to the recombination process is studied in a theoretical model. The geographical structure of the model is a stepping-stone chain of populations linking two genetically constant source populations. The model assumes an arbitrary number of autosomal loci and considers genetic variation (two alleles at each locus) that is not subject to natural selection. The gene frequencies at each locus will then show a linear cline through the stepping-stone chain of populations. The deviation from linkage equilibrium through the stepping-stone cline is characterized by an equation for linear measures that provide the linkage disequilibrium measures for a given set of loci in terms of the gene frequencies and the linkage disequilibria in the source populations and in terms of the linkage disequilibrium measures through the cline for lower numbers of loci. Numerical examples of this iterative solution are given, and it is shown that the build-up of the higher order Bennett-disequilibria through the cline is considerably more pronounced than the build-up of two-locus disequilibria.     

N-succinimidyl methoxyphenylacetic acid ester, an amine-directed chiral derivatizing reagent suitable for enzymatic scale resolutions

A chiral derivatizing reagent, N-succinimidyl-2-(S)-methoxy-2-phenylacetic acid ester (SMPA), directed toward reaction with primary amine-containing compounds has been synthesized and characterized. This reagent is suitable for HPLC resolution from enzymatic-scale reactions where only microgram quantities of chiral products may be obtainable. SMPA derivatization was shown to be effective in the resolution of the enantiomers of a number of different racemic compounds. SMPA was used to resolve the diastereoisomeric derivatives of a previously unknown enzymatically oxygenated product, allowing determination of the stereochemical course of the enzymatic reaction. SMPA is easily prepared from an inexpensive, commercially available, and enantiomerically pure precursor with the formation of a shelf-stable crystalline product which is utilizable in water-containing solutions. In addition to its usefulness for micro-determinations, SMPA is useful for preparative-scale resolutions of enantiomers since the reagent is cleaved from the diastereoisomeric derivative by acid hydrolysis.     

Instability of orthophthalaldehyde reagent for amino acid analysis

Determination of amino acids by reversed-phase chromatography of the adduct with orthophthalaldehyde and a thiol is rapid and sensitive. The major recognized adverse feature of this method is the instability of the reaction product, which requires precise control of reaction timing and chromatographic parameters for reliable quantitative application. We report another source of major variability: reagent instability. Deterioration of reagent was noted as low peak heights and peak broadening and was predictable if the premixed reagent was left at room temperature. Restoration of sharp chromatograms was accomplished by addition of mercaptoethanol or sodium metabisulfite. Reagent which was chromatographically inert contained minimal free thiol by direct assay. Free thiol disappearance was markedly slowed by addition of a chelating agent. Excess mercaptoethanol was deleterious. We conclude that reagent deterioration represents oxidation of the thiol, may be reversed by rereduction with minimal thiol or bisulfite, and may be minimized by inclusion of a metal chelator in the reagent.     

Demonstration of the ascorbate dependence of membrane-bound dopamine beta-monooxygenase in adrenal chromaffin granule ghosts

Chromaffin granule ghosts from bovine adrenal medullae have been used to examine the ability of membrane-bound dopamine beta-monooxygenase to interact directly with intravesicular ascorbate and to investigate vectorial electron transfer from external ascorbate across the ghost membrane. Ghosts prepared by a modification of published procedures were shown to be fully active in both dopamine uptake and norepinephrine production. Dopamine uptake is dependent on the presence of a magnesium and ATP ionic complex, is abolished by reserpine, and reaches a steady-state level in the presence of dopamine beta-monooxygenase, ascorbate, catalase, and fumarate. Omission of ascorbate either inside or outside the ghosts greatly enhances dopamine accumulation, which reaches levels of approximately 30 nmol/mg under these conditions. Correspondingly, in the presence of all components, norepinephrine production reached approximately 100 nmol/mg in 30 min of incubation. Norepinephrine production was strictly magnesium-ATP-dependent, inhibited by either reserpine or dopamine beta-monooxygenase inactivation, and was markedly reduced when ascorbate was omitted from either inside or outside the ghosts. In the presence of limiting amounts of internal ascorbate, rapid norepinephrine production occurred which corresponded to the amount of initial ascorbate present, followed by a much slower endogenous norepinephrine production observable after complete depletion of internal ascorbate. The endogenous rate of norepinephrine production likely represents epinephrine-supported dopamine beta-monooxygenase turnover. Taken together, the data demonstrate that facile norepinephrine production by membrane-bound dopamine beta-monooxygenase occurs only when internal ascorbate is present, terminates upon depletion of internal ascorbate, and can only be sustained at a significant rate when reducing equivalents from external ascorbate are available.     

Inter-protein distances within the large subunit from Escherichia coli ribosomes.

Selected pairs of protonated ribosomal proteins were reconstituted into deuterated 50S subunits from Escherichia coli ribosomes. The rRNA of the deuterated ribosomal matrix was derived from cells grown in 76% D2O, the deuterated protein moiety from cells grown in 84% D2O. This procedure warrants that the coherent neutron scattering of deuterated proteins and rRNA is nearly the same and equals that of a D2O solution of approximately 90%. The neutron scattering is recorded in a reconstitution buffer containing approximately 90% D2O. The result is a significant improvement of the coherent signal:noise ratio over traditional methods; due to this dilute solutions can be used, thus preventing unfavorable inter-particle effects. From the diffraction pattern the distance between the mass centers of gravity of the two protonated proteins can be deduced. In this way, 50 distances between proteins within the large subunit have been determined which provide a basis for future models of the large ribosomal subunit describing the spatial distribution of the ribosomal proteins. A model containing seven ribosomal proteins is presented.