ascorbic-acid and 3-hydroxyaspartic-acid

A recently described in vivo voltammetric electrode selectively records rapid changes in extracellular fluid (ECF) levels of ascorbic acid. Using this detector, the nature of glutamate-induced efflux of ascorbate into ECF was investigated using pharmacological tools. Ascorbate signals were shown to be directly related to amounts of microinjected glutamate. Blockers of glutamate reuptake, homocysteic acid and D,L-threo-beta-hydroxy-aspartic acid, virtually eliminate the ascorbate signal. A more specific reuptake blocker (the stilbene isothiocyano derivative (SITS) does not completely inhibit ascorbate efflux, suggesting that the glutamate uptake which is coupled to ascorbic acid exchange is both neuronal and glial in nature. Other pharmacological experiments indicate that excitatory amino acid receptors are not involved in the glutamate-elicited ascorbate efflux; it is primarily a function of the glutamate/ascorbate heteroexchange process as described earlier. The possible role(s) of brain ascorbate in the general functioning of the pervasive glutamate neurotransmitter systems are discussed.

Topics: 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; Animals; Ascorbic Acid; Aspartic Acid; Brain; Corpus Striatum; Electric Stimulation; Electrochemistry; Globus Pallidus; Glutamates; Glutamic Acid; Hippocampus; Kynurenic Acid; Male; Microinjections; N-Methylaspartate; Organ Specificity; Potentiometry; Rats; Rats, Inbred Strains; Stereotaxic Techniques; Thalamus

beta- Hydroxyaspartic acid is a rare amino acid, present in all vitamin K-dependent plasma proteins except prothrombin, and is formed by a post-translational hydroxylation of aspartic acid. We have now investigated whether this hydroxylation, like that of proline in collagen, is vitamin C-dependent. The vitamin K-dependent plasma proteins were isolated from normal and scorbutic guinea pig plasma by barium citrate adsorption and the beta- hydroxyaspartic acid content was determined. Compared with normal animals, scorbutic animals showed no significant reduction of beta- hydroxyaspartic acid content. In warfarin-treated animals there was a decreased content of both beta- hydroxyaspartic acid and gamma-carboxyglutamic acid in the barium citrate adsorbed fraction. It was concluded that the post-translational hydroxylation of aspartic acid is unlikely to be vitamin C-dependent.

Topics: 1-Carboxyglutamic Acid; Animals; Ascorbic Acid; Ascorbic Acid Deficiency; Aspartic Acid; Blood Coagulation; Blood Proteins; Guinea Pigs; Hydroxylation; Protein Processing, Post-Translational; Vitamin K; Warfarin