Lactobacillus arabinosus, amino acid

The uptake and accumulation of various amino acids in Lactobacillus arabinosus have been described. Deficiencies of vitamin B6, biotin, and pantothenic acid markedly alter the operation of these transport systems. Accumulation capacity is decreased most severely by a vitamin B6 deficiency. This effect appears to arise indirectly from the synthesis of abnormal cell wall which renders the transport systems unusually sensitive to osmotic factors. Kinetic and osmotic experiments also exclude biotin and pantothenate from direct catalytic involvement in the transport process. Like vitamin B6, they affect uptake indirectly, probably through the metabolism of a structural cell component. The evidence presented supports a concept of pool formation in which free amino acids accumulate in the cell through the intervention of membrane-localized transport catalysts. 

General Characteristics of Amino Acid Transport in Lactobacillus Transport in Lactobacillus arabinosus... 

The experiments discussed were performed with Lactobacillus arabinosus using glutamic acid, alanine, and proline as the test amino acids. The detailed experimental procedures have been described (21, 23, 27). Washed resting cells are incubated in a phosphate buffer with the radioactive amino acid, centrifuged, and extracted to release the amino acid, which is then measured enzymically or by isotopic methods. 

Alanine isolated by mild alkaline hydrolysis from the teichoic acid of Lactobacillus arabinosus has the d configuration, as determined with D-amino acid oxidase. ... 

Hegsted, D. M. The Amino Acid Requirement of Lactobacillus arabinosus. 

The existence of enzymes in microorganisms which catalyze the interconversion of D- and L-amino acids is of considerable interest, since the intramolecular transfer of an amino group is apparently involved. The term racemase has been proposed for such enzymes. Two racemases have been reported. Alanine racemase has been shown to be present in a large number of microorganisms and has been partially purified from extracts of S. faecalis. Glutamic acid racemase has been demonstrated in acetone powders of Lactobacillus arabinosus. Both enzymes catalyze the interconversion of the n- and l- forms of their respective substrates. Alanine racemase requires pyridoxal phosphate as coenzyme. Pyri-doxamine phosphate under the conditions employed was not active. Glutamic acid racemase was found not to be affected by the addition of pyridoxal phosphate. However, further studies with purified preparations are necessary before pyridoxal phosphate can be excluded as cofactor for the glutamic acid racemase. Examination of animal tissues under conditions favorable for the demonstration of bacterial alanine racemase failed to reveal any activity. 

Shiota (11a) obtained cell-free extracts of Lactobacillus arabinosus which were capable of synthesizing folic acid activity when the extracts were incubated with 2-amino-4-hydroxy-6-hydroxymethyl-5,6,7,8-tetrahydro-pteridine and PABG. The system was dependent on adenosine triphosphate (ATP) and Mg++. The folic acid activity of the reaction mixture was demonstrated by bioautography with Streptococcus faecalis and the chromatogram indicated a mixture of a reduced form of folic acid (the chromatographic system did not distinguish between dihydrofolic acid and FH4) and folic acid, ihe latter possibly arising by oxidation. 

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