Proceedings of the National Academy of Sciences of the United States of America
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Proc. Natl. Acad. Sci. U.S.A. · Jan 1978
Deoxyadenosine triphosphate as a potentially toxic metabolite in adenosine deaminase deficiency.
The inherited deficiency of adenosine deaminase (adenosine aminohydrolase; EC 3.5.4.4) activity in humans is associated with an immunodeficiency. Some of the immunodeficient and enzyme-deficient patients respond immunologically to periodic infusions of irradiated erythrocytes containing adenosine deaminase. ⋯ The erythrocyte dATP in two unrelated adenosine deaminase-deficient, immunodeficient patients disappeared after infusion of normal erythrocytes. We propose that deoxyadenosine, a substrate of adenosine deaminase, is the potentially toxic substrate in adenosine deaminase deficiency, and that the mediator of the toxic effect is dATP, a recognized potent inhibitor of ribonucleotide reductase.
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Proc. Natl. Acad. Sci. U.S.A. · Sep 1975
Brain tryptophan hydroxylase: purification of, production of antibodies to, and cellular and ultrastructural localization in serotonergic neurons of rat midbrain.
Tryptophan hydroxylase [EC 1.14.16.4; L-tryptophan, tetrahydropteridine:oxygen oxidoreductase (5-hydroxylating)], the enzyme catalyzing the rate-limiting step in the biosynthesis of serotonin, was purified 79-fold from the region of the raphe nucleus of rat midbrain by sequential column chromatography and disc-gel electrophoresis. In electrophoresis three bands were distinguished, A, B, and C, which, when separated and submitted individually to electrophoresis, reproduced the same three bands. Bands A and C were enzymatically active and inhibited by para-chlorohenylalanine. ⋯ Ultrastructurally, in cell bodies, the enzyme was distributed in cytoplasm and in association with endoplasmic reticulum and Golgi apparatus. In dendrites and axons, it was associated with microtubules. Tryptophan hydroxylase in brain is only neuronal and cytoplasmic, exists in multiple forms, and is associated with microtubules, suggesting it may be transported from sites of synthesis in cell body into axons.
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X-ray diffraction studies have produced a low resolution image and also located the iron atoms of a monomeric hemerythrin from muscles of a sipunculan worm. These results reveal the course of the polypeptide chain and some details of the active center.
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Proc. Natl. Acad. Sci. U.S.A. · Nov 1974
A manyfold increase in sister chromatid exchanges in Bloom's syndrome lymphocytes.
Dividing cells from persons with Bloom's syndrome, an autosomal recessive disorder of growth, exhibit increased numbers of chromatid breaks and rearrangements. A highly characteristic feature of the chromosome instability in this syndrome is the tendency for exchanges to occur between chromatids of homologous chromosomes at homologous sites. In the present experiments, a cytogenetic technique by which the sister chromatids of a metaphase chromosome are stained differentially has been used to demonstrate a striking and possibly specific, but hitherto unrecognized, increase in the frequency with which sister chromatids also exchange segments. ⋯ By following shifts in the pattern of staining from chromatid to chromatid, visual evidence was obtained that the quadriradial configurations long recognized as characteristic of Bloom's syndrome represent exchanges between homologous chromosomes, apparently at homologous points. We postulate that the increase in the frequency of exchanges between nonsister-but-homologous chromatids and those between sister chromatids in Bloom's syndrome represents aspects of one and the same disturbance. A study of this phenomenon in relation to the clinical features of Bloom's syndrome may be helpful eventually in understanding the biological significance of chromatid exchange in somatic cells.
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Proc. Natl. Acad. Sci. U.S.A. · Nov 1970
220 MHz proton nuclear magnetic resonance study of the interaction between chicken M4 lactate dehydrogenase and reduced diphosphopyridine nucleotide.
220 MHz proton nuclear magnetic resonance investigations of reduced pyridine coenzymes and coenzyme fragments, both in the presence and absence of M(4) lactate dehydrogenase, show the following: (1) That the energy barrier between a folded and open conformation of the reduced pyridine coenzyme (in aqueous solutions) is insignificant because an unfavorable enthalpy change of 5 kcal is compensated for by a favorable entropy change of 19 entropy units. (2) The coenzyme, however, appears to maintain its intramolecularly folded conformation on contact with the enzyme. The binding of the coenzyme results in the immobilization of the adenine and pyridine moieties and there is no longer any gain in the conformational entropy as a result of unfolding as in aqueous solutions. (3) The purine moiety of the coenzyme facilitates the binding of the pyridine ring and indicates how high frequency nuclear magnetic resonance can be utilized to study binding of small molecules to enzymes.