Maternal factors in onset of Huntington disease.

Analyses of father-offspring and mother-offspring similarity in onset age suggest that nuclear genes account for a significant portion of the modification of onset age in Huntington disease. The effects of non-nuclear modifiers are supported by the finding that the offspring of affected women have significantly older mean ages of onset than offspring of affected men irrespective of the onset age in the parent. The absence of increased father-daughter similarity indicates that modification is not X-linked. The absence of reproductive advantage for late-onset individuals and the absence of a multigenerational maternal-lineage effect suggest that the modifying effect of the sex of the affected parent occurs in a single parental generation. Offspring of affected women with onset between ages 35 and 49 had a significantly older mean onset age than their mothers. This suggests that a protective effect may be conferred upon the offspring of affected women.     

Effect of vitamin B-6 (pyridoxine) deficiency on lung elastin cross-linking in perinatal and weanling rat pups.

Weanling and perinatal rats were rendered vitamin B-6 (pyridoxine)-deficient. The rat pups were nursed from vitamin B-6-deficient or -sufficient dams and were killed at day 15 after parturition. The weanling rats were fed vitamin B-6-deficient or -sufficient diets and were killed after 5 weeks of treatment. Lung elastin from the groups of rats was then studied with respect to its content of lysine-derived cross-linking amino acids. Lung lysyl oxidase activity was also measured. B-6 deficiency decreased the number of lysine residues in elastin that were converted into the cross-linking amino acid precursor allysine. However, a more significant defect in cross-link formation was an apparent block in the condensation steps leading to the formation of desmosine. Desmosine was decreased, with an increase in the amounts of aldol condensation products (aldol CP) in elastin. It is proposed that the elevation in aldol CP results from the formation of thiazines, which are produced from the reaction between aldehyde and homocysteine. The concentration of homocysteine is significantly elevated in vitamin B-6-deficient rats.     

The Kok Effect in Chlamydomonas reinhardi

A Haxo-Blinks rate-measuring oxygen electrode together with a modulated light source gave an average current signal (change in net O₂ exchange) and a modulated current signal (photosynthetic O₂ evolution). Using this apparatus, net O₂ exchange and photosynthetic O₂ evolution at low intensities have been studied in the green alga, Chlamydomonas reinhardi. At both 645 nm and 695 nm, the curves of net O₂ exchange as a function of light intensity were steeper at lowest intensities than about compensation, indicative of the Kok effect. The effect was greater at 695 nm than at 645 nm. The corresponding curves of photosynthetic O₂ evolution, on the other hand, showed no Kok effect; here, the slope was lowest at lowest intensity. The absence of the Kok effect in O₂ evolution, together with its sensitivity to monofluoroacetic acid, show that it is due to an interaction of photosynthesis and respiration. The effect was exaggerated by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. In the presence of concentrations of this inhibitor sufficient to inhibit O₂ evolution completely, a light-induced change in net O₂ exchange remained. This was interpreted as a system I dependent depression of respiratory O₂ uptake. The Kok effect remained undiminished in concentrations of carbonyl cyanide m-chlorophenylhydrazone and 2,4-dinitrophenol which partially uncoupled either oxidative phosphorylation alone or both oxidative and photosynthetic phosphorylations. The above results can be explained within a model of the Kok effect in which O₂ uptake is depressed by diversion of reductant away from respiratory electron transport and into photosystem I. The same photodepression of O₂ uptake also appears to account for a transient in net O₂ exchange seen in several algae upon turning off the light.     

Sweat Chlorides in Salt-Deprived Cystic Fibrosis Heterozygotes

Sweat chlorides of 10 sets of parents of children with cystic fibrosis and 11 controls were studied in an attempt to develop a test for the diagnosis of cystic fibrosis heterozygotes by subjecting both the parents and controls to a low sodium diet and comparing sweat chloride values as the diet progressed. It was hoped that the sweat chloride levels of the parents, the heterozygotes, would remain stationary throughout the diet, since their children, the homozygotes, reveal this finding under similar conditions of salt deprivation. The sweat chloride levels of the controls, because of effects of aldosterone, were expected to decrease steadily from the commencement of the diet to its termination.A decrease in sweat chloride values of similar magnitude was found in both parents and controls as the diet continued. It is concluded that the study of sweat electrolyte levels in salt-deprived subjects is of no value in the diagnosis of cystic fibrosis heterozygotes.     

Spatial proximity and sequence localization of the reactive sulfhydryls of porphobilinogen synthase.

The zinc metalloenzyme porphobilinogen synthase (PBGS) contains several functionally important, but previously unidentified, reactive sulfhydryl groups. The enzyme has been modified with the reversible sulfhydryl-specific nitroxide spin label derivative of methyl methanethiosulfonate (MMTS), (1-oxyl-2,2,5,5-tetramethyl-delta 3-pyrroline-3-methyl)methanethiosulfonate (SL-MMTS) (Berliner, L. J., Grunwald, J., Hankovszky, H. O., & Hideg, K., 1982, Anal. Biochem. 119, 450-455). EPR spectra show that SL-MMTS labels three groups per PBGS subunit (24 per octamer), as does MMTS. EPR signals reflecting nitroxides of different mobilities are observed. Two of the three modified cysteines have been identified as Cys-119 and Cys-223 by sequencing peptides produced by an Asp-N protease digest of the modified protein. Because MMTS-reactive thiols have been implicated as ligands to the required Zn(II), EPR spectroscopy has been used to determine the spatial proximity of the modified cysteine residues. A forbidden (delta m = 2) EPR transition is observed indicating a through-space dipolar interaction between at least two of the nitroxides. The relative intensity of the forbidden and allowed transitions show that at least two of the unpaired electrons are within at most 7.6 A of each other. SL-MMTS-modified PBGS loses all Zn(II) and cannot catalyze product formation. The modified enzyme retains the ability to bind one of the two substrates at each active site. Binding of this substrate has no influence on the EPR spectral properties of the spin-labeled enzyme, or on the rate of release of the nitroxides when 2-mercaptoethanol is added.(ABSTRACT TRUNCATED AT 250 WORDS)     

Gas Chromatography-Mass Spectrometry of N- Heptafluorobutyryl Isobutyl Esters of Amino Acids in the Analysis of the Kinetics of [N]H(4) Assimilation in Lemna minor L

Rapid, sensitive, and selective methods for the determination of the ¹⁵N abundance of amino acids in isotopic tracer experiments with plant tissues are described and discussed. Methodology has been directly tested in an analysis of the kinetics of [¹⁵N]H₄⁺ assimilation in Lemna minor L. The techniques utilize gas chromatography-mass spectrometry selected ion monitoring of major fragments containing the N moiety of N-heptafluorobutyryl isobutyl esters of amino acids. The ratio of selected ion pairs at the characteristic retention time of each amino acid derivative can be used to calculate ¹⁵N abundance with an accuracy of ±1 atom% excess ¹⁵N using samples containing as little as 30 picomoles of individual amino acids. Up to 11 individual amino acid derivatives can be selectively monitored in a single chromatogram of 30 minutes. It is suggested that these techniques will be useful in situations where the small quantities of N available for analysis have hitherto hindered the use of ¹⁵N-labeled precursors.     

Binding of adenosine 3',5'-monophosphate dependent protein kinase regulatory subunit to immobilized cyclic nucleotide derivatives.

Several cyclic nucleotide derivatives with aminoalkyl side chains attached to the purine ring were synthesized and their interactions with adenosine 3',5'-monophosphate (cAMP) dependent protein kinase were studied before and after immobilization to CNBr-activated Sepharose 4B. The soluble N6-substituted derivatives were as effective as cAMP itself in activating protein kinase and were more effective than 8-substituted cAMP derivatives, whereas the 2-substituted cAMP derivatives and the cGMP derivatives were the least effective. All of the synthetic derivatives tested were poor substrates for beef heart phosphodiesterase being hydrolyzed at rates less than 2% for that of cAMP itself. Utilizing methodology developed to evaluate the affinity of protein kinase for immogilized cyclic nucleotides it was found that all of the immobilized cyclic nucleotides interacted with protein kinase in a biospecific manner as judged by the following criteria: (1) the immobilized cyclic nucleotides competed with cAMP for the binding sites on protein kinase; (2) the analogous spacer-arm did not compete; and (3) the effects of enzyme concentration, MgATP, and cleavage of the cyclic phosphate ring on the interactions of protein kinase with the immobilized cyclic nucleotides were the same as previously shown for free cAMP. In addition, the immobilized ligands were bound with the same order of effectiveness as the analogous soluble ligand. The observed Ka for the activation of 0.005 muM protein kinase by N6-H2N(CH2)2-cAMP was increased from 0.23 to 3 muM by the process of immobilization. This increase was unaffected by the coupling density and spacer-arm length. The observed Kb for 0.10 muM protein kinase binding to immobilized N6-H2N(CH2)2-cAMP was increased as the molecular sieving exclusion limit of the matrix used was decreased indicating that at least part of this decrease in apparent affinity upon immobilization is due to exclusion of the enzyme from a portion of the matrix and therefore of the immobilized ligand molecules.