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Biomedical subjects

J W Thanassi

Publications and source records attributed to J W Thanassi.

33 records · Page 2Linked to original sources
PubMed1980

A radioimmunoassay for phosphorylated forms of vitamin B6.

Hapten-specific antibodies are found in rabbit serum afterimmunization of the animals with phosphopyridoxyl-bovine serum albumin. These were purified approximately 80-fold by salt fractionation and affinity chromatography on phosphopyridoxyl-aminoethyl cellulose. The purified hapten-specific antibodies were covalently coupled to Immunobeads. The antibody-Immunobead preparation binds [3H]pyridoxine phosphate. This provides the basis for a radioimmunoassay for vitamin B6 derivatives. [3H]Pyridoxine phosphate is displaced from the matrix-attached antibodies by pyridoxine phosphate, pyridoxamine phosphate, and pyridoxal phosphate, but is not displaced to any significant extent by pyridoxine, pyridoxamine, pyridoxal, or 5'-deoxypyridoxal. The antibody-Immunobead preparation may be recycled for reutilization in radioimmunoassay procedures. The sensitivity of the assay is in the picomole range.

Animals↗
PubMed1980

Pyridoxine kinase, pyridoxine phosphate phosphatase and pyridoxine phosphate oxidase activities in control and B-6-deficient rat liver and brain.

The levels of pyridoxal phosphate in plasma, liver and brain and the activities of pyridoxine kinase, pyridoxine phosphate phosphatase and pyridoxine phosphate oxidase in liver and brain were measured over a 6-week period in rats fed pyridoxine-sufficient and pyridoxine-deficient diets. Consistently significant differences in enzyme activities between the two groups of animals were found only in pyridoxine kinase indicating that this enzyme plays a key role during the development of vitamin B-6 deficiency. Relative to control animals, the decrease observed in liver pyridoxine kinase acivity in animals fed pyridoxine-deficient diets is much greater than the decrease in brain pyridoxine kinase activity (50% decrease versus a 14% decrease after 5 weeks). In light of the suggestion that phosphorylation and binding to proteins serve to prevent the diffusion of B-6 vitamers out of cells, the differential response of pyridoxine kinase activity in liver and brain may be important in the maintenance of the vitamin B-6 supply in the central nervous system. During the course of this study, a new method for the determination of cellular phosphatase activity on a phosphorylated form of vitamin B-6 was developed. 3H-C4'-Pyridoxine phosphate was used as substrate and was separated from 3H-C4'-pyridoxine by means of anion-exchange filter paper disks.

Animals↗
PubMed1979

Coenzyme--substrate adducts as inhibitors of mouse liver 3,4-dihydroxyphenylalanine decarboxylase.

N-(5'-Phosphopyridoxyl) derivatives of several aromatic amino acids have been prepared by conventional methods and tested as inhibitors of mouse liver L-3,4-dihydroxyphenylalanine (Dopa) decarboxylase (EC 4.1.1.26; L-aromatic-amino-acid decarboxylase). The L-tyrosine, L-phenylalanine, and DL-2-hydroxyphenylalanine derivatives were effective inhibitors at concentrations of 10(-5) M. Because of the spontaneous formation of a tetrahydroisoquinoline cyclic condensation product with pyridoxal phosphate (Pictet--Spengler reaction), the Dopa derivative could not be prepared by the usual procedures. The synthesis of the desired N-(5'-phosphopyridoxyl)-Dopa was accomplished using selective blocking--deblocking methods; its properties are described. This proved to be the most effective inhibitor of those tested. Neither the tetrahydroisoquinoline of L-Dopa and pyridoxal phosphate nor the N-(5'-deoxypyridoxyl)-Dopa was an effective inhibitor of Dopa decarboxylase. These coenzyme amino acid adducts are suggested to act as stage inhibitors of the enzyme.

Amino Acids↗
PubMed1975

Reactions of aminomalononitrile with electrophiles.

Aminomalononitrile (HCN trimer) reacts with electrophiles such as aldehydes and acrylonitrile under very mild conditions of temperature and pH to produce intermediates which, after acid hydrolysis, yield amino acids. The following amino acids have been identified and quantitated: glycine, D, L-erythro- and D, L-threo-beta - hydroxyaspartic acids, D, L glutamic acid, and D, L-threonine and allo-threonine. The mechanism of their formation and the possible significance of these reactions in prebiotic syntheses are discussed.

Amines↗