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PubMed1976

Phosphopantothenic acid--the major product of pantothenic acid accumulation and a significant growth stimulatn in Lactobacillus plantarum.

Non-proliferating cells of Lactobacillus plantarum accumulated about 1.3 mug of pantothenic acid (PA) per milligram dry cells when placed in a phosphate-buffered solution containing glucose, NaCl, and PA for 21 h. Under the conditions applied for PA uptake, pH 7.5 and 38 degrees C, the accumulated PA existed almost exclusively in a bound form. Free PA was observed only occasionally and then at questionably significant levels. All bound PA was released quantitatively by enzyme hydrolysis with alkaline (intestinal) phosphatase. Chromatographic analysis coupled with differential microbiological analysis of cell extracts using Saccharomyces cerevisiae, Lactobacillus helveticus, and L. plantarum identified the accumulated PA as phosphopantothenic acid (P-PA). Assay of P-PA loaded cell extracts (devoid of free PA) by L. plantarum before and after alkaline phosphatase hydrolysis showed that the growth of this primary assay organism was stimulated by 8.3%.

Alkaline Phosphatase↗
PubMed1983

Role of acetohydroxy acid isomeroreductase in biosynthesis of pantothenic acid in Salmonella typhimurium.

Structural genes have been identified for all of the enzymes involved in the biosynthesis of pantothenic acid in Salmonella typhimurium and Escherichia coli K-12, with the exception of ketopantoic acid reductase, which catalyzes the conversion of alpha-ketopantoate to pantoate. The acetohydroxy acid isomeroreductase from S. typhimurium efficiently bound alpha-ketopantoate (K(m) = 0.25 mM) and catalyzed its reduction at 1/20 the rate at which alpha-acetolactate was reduced. Since two enzymes could apparently participate in the synthesis of pantoate, a S. typhimurium ilvC8 strain was mutagenized to derive strains completely blocked in the conversion of alpha-ketopantoate to pantoate. Several isolates were obtained that grew in isoleucine-valine medium supplemented with either pantoate or pantothenate, but not in the same medium supplemented with alpha-ketopantoate or beta-alanine. The mutations that conferred pantoate auxotrophy (designated panE) to these isolates appeared to be clustered, but were not linked to panB or panC. All panE strains tested had greatly reduced levels of ketopantoic acid reductase (3 to 12% of the activity present in DU201). The capacity of the isomeroreductase to synthesize pantoate in vivo was assessed by determining the growth requirements of ilvC(+) derivatives of panE ilvC8 strains. These strains required either alpha-ketopantoate, pantoate, or pantothenate when the isomeroreductase was present at low levels; when the synthesis of isomeroreductase was induced, panE ilvC(+) strains grew in unsupplemented medium. These phenotypes indicate that a high level of isomeroreductase is sufficient for the synthesis of pantoate. panE ilvC(+) strains also grew in medium supplemented with lysine and methionine. This phenotype resembles that of some S. typhimurium ilvG mutants (e.g., DU501) which are partially blocked in the biosynthesis of coenzyme A and are limited for succinyl coenzyme A. panE ilvC(+) strains which lack the acetohydroxy acid synthases required only methionine for growth (in the presence of leucine, isoleucine, and valine). This and other evidence suggested that the synthesis of pantoic acid by isomeroreductase was blocked by the alpha-acetohydroxy acids and that pantoic acid synthesis was enhanced in the absence of these intermediates, even when the isomeroreductase was at low levels. panE ilvC(+) strains reverted to pantothenate independence. Several of these revertants were shown to have elevated isomeroreductase levels under noninduced and induced conditions; the suppressing mutation in each revertant was shown to be closely linked to ilvC by P22 transduction. This procedure presents a means for obtaining mutants with altered regulation of isomeroreductase.

2-Acetolactate Mutase↗
PubMed1986

Absorption of pantothenic acid in rat and chick intestine.

Pantothenic acid absorption was evaluated in the intestine of rat and chicken to reevaluate the concept that this nutrient crosses the mucosa by simple diffusion. Unidirectional influx of [3H]pantothenic acid (0.9 microM) across the brush-border membrane of rat jejunum in vitro demonstrates sodium dependence and saturation kinetics. Net transepithelial transport (absorption) of pantothenic acid takes place in everted sacs of jejunum against an electrochemical potential gradient. This accumulation does not occur in tissue exposed to metabolic inhibitors. Also, pantothenic acid accumulates in the transport cells of both rat and chicken intestine against a 9- to 10-fold concentration gradient. Recently absorbed pantothenic acid is freely diffusible from isolated chicken enterocytes. No metabolic conversion of pantothenic acid was detected during absorption in the intestine of either species under conditions in vitro or in vivo. The present results indicate that pantothenic acid present at low concentrations is absorbed in the intestine by a specific transport mechanism; the process is best described as sodium-dependent, secondary active transport.

Absorption↗
PubMed1984

Transport and metabolism of pantothenic acid by rat kidney.

Transport of [14C]pantothenic acid was studied using brush-border membrane vesicles prepared from rat kidney. In the presence of a Na+ gradient an accumulation of pantothenic acid 3-fold above equilibrium was observed. The Km and Vmax found were 7.30 microM and 23.8 pmol/mg protein per min, respectively. Isolated perfused rat kidneys were employed to study excretion of pantothenic acid at various concentrations in the perfusate. At physiological plasma concentrations, the filtered pantothenic acid was largely reabsorbed by the active process observed in the vesicles. At higher concentrations, pantothenic acid was found to undergo tubular secretion. Penicillin inhibited this secretory process indicating that both compounds share a secretory mechanism. Live animal studies indicated that the only compound excreted after injection of [14C]pantothenic acid was free pantothenic acid. After 1 week only 38% of the administered dose was excreted in the urine, indicating that effective conservation was taking place in the whole animal.

Animals↗