D-Norvaline

Islets of Langerhans are responsible for maintaining glucose homeostasis through regulated secretion of hormones and other factors. It is hypothesized that amino acids secreted from islets play a critical role in cell functionality and viability. For example, glutamate and gamma-aminobutyric acid have been proposed to work as paracrine signaling molecules within islets to coordinate the release of hormone secretion; other amino acids, such as glutamine, leucine, alanine, and arginine, have been shown to stimulate or potentiate glucose-stimulated insulin secretion. To characterize the potential roles that these small molecules may play in islet physiology, derivatization of amino acids in high-salt buffers commonly used in islet experiments with naphthalene-2,3-dicarboxaldehyde and MEKC separation conditions were optimized. The optimized conditions used d-norvaline as the internal standard and allowed quantification of 14 amino acids with LODs ranging from 0.

Two recombinant reaction systems for the production of optically pure D-amino acids from different D,L-5-monosubstituted hydantoins were constructed. Each system contained three enzymes, two of which were D-hydantoinase and D-carbamoylase from Agrobacterium tumefaciens BQL9. The third enzyme was hydantoin racemase 1 for the first system and hydantoin racemase 2 for the second system, both from A. tumefaciens C58. Each system was formed by using a recombinant Escherichia coli strain with one plasmid harboring three genes coexpressed with one promoter in a polycistronic structure. The D-carbamoylase gene was cloned closest to the promoter in order to obtain the highest level of synthesis of the enzyme, thus avoiding intermediate accumulation, which decreases the reaction rate. Both systems were able to produce 100% conversion and 100% optically pure D-methionine, D-leucine, D-norleucine, D-norvaline, D-aminobutyric acid, D-valine, D-phenylalanine, D-tyrosine, and D-tryptophan from the corresponding hydantoin racemic mixture.

The amino acid L-phenylalanine has been cocrystallized with D-2-aminobutyric acid, C(9)H(11)NO(2).C(4)H(9)NO(2), D-norvaline, C(9)H(11)NO(2).C(5)H(11)NO(2), and D-methionine, C(9)H(11)NO(2).C(5)H(11)NO(2)S, with linear side chains, as well as with D-leucine, C(9)H(11)NO(2).C(6)H(13)NO(2), D-isoleucine, C(9)H(11)NO(2).C(6)H(13)NO(2), and D-allo-isoleucine, C(9)H(11)NO(2).C(6)H(13)NO(2), with branched side chains. The structures of these 1:1 complexes fall into two classes based on the observed hydrogen-bonding pattern. From a comparison with other L:D complexes involving hydrophobic amino acids and regular racemates, it is shown that the structure-directing properties of phenylalanine closely parallel those of valine and isoleucine but not those of leucine, which shares side-chain branching at C(gamma) with phenylalanine and is normally considered to be the most closely related non-aromatic amino acid.

The endocytosis and catabolism of large quantities of host cell hemoglobin is a hallmark of the intraerythrocytic asexual stage of the human malaria parasite Plasmodium falciparum. It is known that the parasite's production of amino acids from hemoglobin far exceeds its metabolic needs. Here, we show that P. falciparum effluxes large quantities of certain non-polar (Ala, Leu, Val, Pro, Phe, Gly) and polar (Ser, Thr, His) amino acids to the external medium. That these amino acids originate from hemoglobin catabolism is indicated by the strong correlation between individual amino acid efflux rates and their abundances in hemoglobin, and the ability of the food vacuole falcipain inhibitor E-64d to greatly suppress efflux rates. We then developed a rapid, sensitive and precise method for quantifying flux through the hemoglobin endocytic-catabolic pathway that is based on leucine efflux. Optimization of the method involved the generation of a novel amino acid-restricted RPMI formulation as well as the validation of D-norvaline as an internal standard.