Computational Investigations of the Chalcogen-Substituted Carboxylic Acids RC(=O)XH and RC(=X)OH and their Dimers [RC(=O)XH]2 and [RC(=X)OH]2 (X=S, Se, Te)

Semiempirical and ab initio theoretical methods have been used to investigate molecular structures of the chalcogen-substituted carboxylic acid isomers RC(=O)XH (chalcogenol acid) and RC(=X)OH (chalcogenon acid). A recent experimental report suggests that the chalcogenon isomers, although less stable at room temperature, predominate at low temperature in polar solvents and that there is only a small barrier to isomerization between the isomers. Theoretical calculations have been used to locate minimum energy structures of chalcogen-substituted carboxylic acid isomers and to calculate energy differences between pairs of isomers. Carboxylic acids are well known to dimerize, especially in the gas phase and in non-polar solvents. We have, therefore, also calculated energies of dimerization of the chalcogen-substituted acids by optimizing the geometries of the symmetric dimers. We note that the PM3 level of theory is only qualitatively correct for sulfur- and selenium-containing species but fails even qualitatively for the tellurium-containing compounds. Ab initio results confirm the experimental observations and provide good estimates of both isomerization and dimerization energies. We conclude that for many functional groups with tautomers RC(=X)YH and RC(=Y)XH, the more acidic tautomer is the one with the acid proton on the smaller, more electronegative atom, although in many cases this may not be the more stable tautomer.Electronic Supplementary Material available.     

Purification and properties of carnitine acetyltransferases from bovine spermatozoa and heart

To investigate the physical and kinetic properties of sperm carnitine acetyltransferase, the enzyme was purified from bovine spermatozoa and heart muscle. Carnitine acetyltransferase was purified 580-fold from ejaculated bovine spermatozoa to a specific activity of 85 units/mg protein (95% homogeneity). Sperm carnitine acetyltransferase was characterized as a single polypeptide of M_r 62,000 and pI 8.2. Heart carnitine acetyltransferase was purified 650-fold by the same procedure to a final specific activity of 71 units/mg protein. The kinetic properties of purified bovine sperm carnitine acetyltransferase were consistent with the proposed function of this enzyme in acetylcarnitine pool formation. Product inhibition by either acetyl-l-carnitine or CoASH was not sufficient to predict significant in vivo inhibition of acetyl transfer. At high concentrations of l-carnitine, bovine sperm and heart carnitine acetyltransferases were most active with propionyl- and butyryl-CoA substrates, although octanoyl-, iso-butyryl-, and iso-valeryl-CoA were acceptable substrates. Binding of one substrate was enhanced by the presence of the second substrate. Carnitine analogs that have significance in reproduction, such as phosphorylcholine and taurine, did not inhibit carnitine acetyltransferase. Bovine sperm and heart carnitine acetyltransferases were indistinguishable on the basis of purification behavior, pI, pH optima, kinetic properties, acyl-CoA specificity, and sensitivity to sulfhydryl reagents and divalent cations; thus there was no indication that bovine sperm carnitine acetyltransferase is a sperm-specific isozyme.     

Specificity of compaction in meiotic chromosomes of the female Chinese hamster

This study describes the sequential alternation of compaction and decompaction in the chromosomes of the Chinese hamster oocyte from diakinesis to metaphase II. A series of micrographs show that the compact metaphase I chromosomes become greatly extended as they enter and pass through anaphase I. Once polarized, the presumptive oocyte chromosomes become exceedingly compact and form a tightly packed mass, each chromosome assuming contours to accomodate dovetailing with its neighbors, while the chromosomes consigned to the polar body remain extended and show signs of the incipient deterioration. Prior to ovulation, the chromosomes of the mass separate and begin to decompact, in part at least, by the previously postulated mechanism of uncoiling. Following ovulation, the chromosomes are greatly extended and, as the metaphase II complement, remain in that state until the advent of fertilization. — Evidence that the compaction patterns are ordered and chromosome specific is presented by observation of the two smallest chromosomes of the complement. At telophase I those chromosomes are markedly different in size and arm ratio; at metaphase II the differences are less pronounced and at mitotic metaphase the two smallest chromosome pairs are so similar in morphology as to be indistinguishable. It is proposed, therefore, that those two chromosomes differ in their fundamental morphology as revealed at the exceedingly compact state of telophase I oocyte chromosomes. Their subsequently established resemblance at mitotic metaphase may be due to allocycly on the part of one or both, resulting in two chromosomes of apparantly similar length and arm ratio.Supported by grants from the Institute of Child Health and Development of the National Institutes of Health, 5 RO1 HDO4846 and the Damon Runyan Foundation, DRG-907.Supported in part by CA-08748 from the Cancer Institute of the National Institutes of Health.     

A recombination outside the BB deletion refines the location of the X linked retinitis pigmentosa locus RP3.

Genetic loci for X-linked retinitis pigmentosa (XLRP) have been mapped between Xp11.22 and Xp22.13 (RP2, RP3, RP6, and RP15). The RP3 gene, which is responsible for the predominant form of XLRP in most Caucasian populations, has been localized to Xp21.1 by linkage analysis and the map positions of chromosomal deletions associated with the disease. Previous linkage studies have suggested that RP3 is flanked by the markers DXS1110 (distal) and OTC (proximal). Patient BB was thought to have RP because of a lesion at the RP3 locus, in addition to chronic granulomatous disease, Duchenne muscular dystrophy (DMD), mild mental retardation, and the McLeod phenotype. This patient carried a deletion extending approximately 3 Mb from DMD in Xp21.3 to Xp21.1, with the proximal breakpoint located approximately 40 kb centromeric to DXS1110. The RP3 gene, therefore, is believed to reside between DXS1110 and the proximal breakpoint of the BB deletion. In order to refine the location of RP3 and to ascertain patients with RP3, we have been analyzing several XLRP families for linkage to Xp markers. Linkage analysis in an American family of 27 individuals demonstrates segregation of XLRP with markers in Xp21.1, consistent with the RP3 subtype. One affected mate shows a recombination event proximal to DXS1110. Additional markers within the DXS1110-OTC interval show that the crossover is between two novel polymorphic markers, DXS8349 and M6, both of which are present in BB DNA and lie centromeric to the proximal breakpoint. This recombination places the XLRP mutation in this family outside the BB deletion and redefines the location of RP3.     

The Differentiation of a Cell Sorting Mutant of Dictyostelium discoideum

As a result of transfecting Dictyostelium discoideum with an actin 6/ lac Z fusion transgene, strain HW80 was created which expresses the β-galactosidase gene product uniformly throughout development. When mixed with an excess of unmarked wild-type cells, however, HW80 cells selectively migrate to the positions of anterior-like cells surrounding the prespore cell mass, and differentiate as if they were anterior-like cells. As the proportion of HW80 cells is increased, they also sort to positions adjacent to anterior-like cells and some differentiate as prespore cells. Thus sorting of HW80 cells toward the opposite ends of the prespore cell zone supersedes how they differentiate, suggesting that position influences whether cells differentiate as anterior-like or prespore cells.