Genetical studies onOenothera. V.

Molecular Genetics and Genomics -     

Cytogenetic studies of three triazine herbicides. I. In vitro studies

Atrazine, simazine, and cyanazine are widely used pre-emergence and post-emergence triazine herbicides that have made their way into the potable water supply of many agricultural communities. Because of this and the prevalence of contradictory cytogenetic studies in the literature on atrazine, simazine, and cyanazine, a series of in vitro experiments was performed to investigate the ability of these three triazines to induce sister chromatid exchanges (SCEs) and chromosome aberrations (CAs) in human lymphocyte cultures. Our results showed that all three triazines failed to produce any significant increases in SCEs or CAs up to the limits of solubility [using 0.5% dimethyl sulfoxide (DMSO)]. Our results are discussed in light of contradictory results in the literature.     

Chicken fumarase. II. Kinetic studies.

The catalysis of the hydration of fumarate and deshydration of L - malate by chicken fumarase was measured spectrophotometrically over a range of substrate concentrations from 4 times 10(-3) M to 8 times 10(-5) M for fumarate and from 8 times 10(-2) M to 10(-3) M for L - malate. For the forward and reverse reactions, linear Lineweaver and Burk plots were obtained. The Michaelis constants and the maximum initial velocities for both substrates were determined and the Haldane relation was found to be obeyed. The effect of pH on activity was investigated over a pH range from 5.5 to 9.0 and the data indicate the presence, in the active site, of two ionizable groups, one in the acidic form and one in the basic form. The values of the ionization constants, determined for the enzyme - substrate complexes, agree closely with the ones obtained for the porcine enzyme. The mode of action of twenty-four structural analogs on the initial velocity of the dehydration of L-malate, by chicken fumarase was examined. From these studies, two regions positively charged appear necessary for the effective binding of the carboxylates of the substrates and competitive inhibitors to the active center. Moreover, the data suggest the presence of an additional group, in the catalytic site of chicken fumarase, that stabilizes the carbon-carbon double bond common to fumarate and its structural analogs. Finally, from the comparison of the kinetic properties of the chicken and pig fumarases, it may be concluded that the catalytic mechanism of the homologous enzymes are very similar, if not identical.     

Saccharopine dehydrogenase. Substrate inhibition studies.

In the direction of reductive condensation of alpha-ketoglutarate and lysine, saccharopine dehydrogenase (N6-(glutar-2-yl)-L-lysine:NAD oxidoreductase (lysine-forming) is inhibited by high concentrations of alpha-ketoglutarate and lysine, but not by NADH. NAD+ and saccharopine show no substrate inhibition in the reverse direction. Substrate inhibition by alpha-ketoglutarate and lysine is linear uncompetitive versus NADH. However, when the inhibition is examined with alpha-ketoglutarate or lysine as the variable substrate, the double reciprocal plots show a family of curved lines concave up. The curvature is more pronounced with increasing concentrations of the inhibitory substrate, suggesting an interaction of variable substrate with the enzyme form carrying the inhibitory substrate. These inhibition patterns, the lack of interaction of structural analogs of lysine such as ornithine and norleucine with the E-NAD+ complex (Fujioka M., and Nakatani, Y. (1972) Eur. J. Biochem. 25, 301-307), the identity of values of inhibition constants of alpha-ketoglutarate and lysine obtained with either one as the substrate inhibitor, and the substrate inhibition data in the presence of a reaction product, NAD+, are consistent with the mechanism that substrate inhibition results from the formation of a dead-end E-NAD+-alpha-ketoglutarate complex followed by the addition of lysine to this abortive complex.     

Allan-Herndon syndrome. I. Clinical studies.

A large family with X-linked mental retardation, originally reported in 1944 by Allan, Herndon, and Dudley, has been reinvestigated. Twenty-nine males have been affected in seven generations. Clinical features include severe mental retardation, dysarthria, ataxia, athetoid movements, muscle hypoplasia, and spastic paraplegia with hyperreflexia, clonus, and Babinski reflexes. The facies appear elongated with normal head circumference, bitemporal narrowing, and large, simple ears. Contractures develop at both small and large joint. Statural growth is normal and macroorchidism does not occur. Longevity is not impaired. High-resolution chromosomes, serum creatine kinase, and amino acids are normal. This condition, termed the Allan-Herndon syndrome, appears distinct from other X-linked disorders having mental retardation, muscle hypoplasia, and spastic paraplegia.     

Significance of retrospective studies.

Examples of retrospective studies are presented to demonstrate some facets of such studies, both good and bad, pointing out the need for good controls. Also important are a clear idea of the question to be answered, and careful planning around that answer as the study progresses.     

Longevity studies in GenomEUtwin.

Previous twin studies have indicated that approximately 25% of the variation in life span can be attributed to genetic factors and recent studies have also suggested a moderate clustering of extreme longevity within families. Here we discuss various definitions of extreme longevity and some analytical approaches with special attention to the challenges due to censored data. Lexis diagrams are provided for the Danish, Dutch, Finnish, Italian, Norwegian, and Swedish Twin registries hereby outlining possibilities for longevity studies within GenomEUtwin. We extend previous analyses of lifespan for the Danish 1870-1900 twin cohorts to include the new 1901-1910 cohorts, which are consistent with the previous findings. The size of the twin cohorts in GenomEUtwin and the existence of population-based, nationwide health and death registers make epidemiological studies of longevity very powerful. The combined GenomEUtwin sample will also allow detailed age-specific heritability analyses of lifespan. Finally, it will provide a resource for identifying unusual sibships (i.e., dizygotic twin pairs) where both survived to extreme ages, as a basis for discovering genetic variants of importance for extreme survival.