1. Coupling of alanine racemase and D-alanine dehydrogenase to active transport of amino acids in Escherichia coli B membrane vesicles
G Kaczorowski, L Shaw, M F-entes, C Walsh J Biol Chem. 1975 Apr 25;250(8):2855-65.
Isolated membrane vesicles from Escherichia coli B grown on DL-alanine-glycerol carry out amino acid active transport coupled to D-alanine oxidation by a membrane-bound dehydrogenase. Several other D-amino acids are substrates for this D-alanine dehydrogenase and also drive concentrative uptake of solutes. Additionally, L-alanine and L-serine can energize solute transport by virtue of conversion to oxidizable D isomers by a membrane-bound alanine racemase. No other physiological L-amino acids were effective. Both membrane enzymes and consequent solute transport are markedly reduced in vesicles from glucose-grown cells. Respiratory chain uncouplers abolish the racemase-dehydrogenase-supported transport activity. When amino-oxyacetate at 10-4 M is added to the vesicles, the racemase activity and transport driven by L-alanine and L-serine is specifically and reversibly inhibited. D-Alanine-driven transport is unaffected. Similarly beta-chloro-L-alanine is an irreversible inactivator of the bound racemase but not the D-alanine dehydrogenase. Both the D and L isomers of beta-chloroalanine support oxygen uptake by the vesicles and initially stimulate L-(14C)proline active transport. However, oxidation of the beta-chloro-D-alanine rapidly uncouples active transport from substrate oxidation. This transport inactivation can be protected partially by dithiothreitol, putatively scavenging a reactive product of chloroalanine oxidation. Authentic beta-chloropyruvate produces the same transport uncoupling. When beta-chloro-L-alanine is employed as a substrate, no such transport inactivation is observed. This difference may stem from the possibility that the alanine racemase eliminates HCl from beta-chloro-L-alanine producing pyruvate, not the beta-chloropyruvate that would arise from racemization and then dehydrogenation. We have shown that exogenous pyruvate is oxidized by the vesicles and will also stimulate active transport of amino acids.
2. Enzymatic transformations of 3-chloroalanine into useful amino acids
T Nagasawa, H Yamada Appl Biochem Biotechnol. 1986 Oct;13(2):147-65. doi: 10.1007/BF02798908.
The investigation of the combination of enzymatic and chemical synthetic processes for the production of useful compounds has been carried out. This review focuses on the enzymatic transformation of chemically synthesized 3-chloroalanine into useful amino acids.
