Herman C. Lichstein

Functions of biotin in enzyme systems.

Publisher Summary This chapter describes the functions of biotin in enzyme systems. Biotin serves an important role in several enzyme systems, namely the decarboxylases of oxalacetate and succinate, the deaminases of aspartic acid, serine, and threonine, succinic acid dehydrogenase, and the synthesis of citrulline. In addition to these functions, this vitamin is somehow related to carbohydrate and fatty acid metabolism and to the amino acid oxidases. Delwiche has presented data demonstrating that biotin is concerned with the decarboxylation of succinic acid to propionic acid. He employed a strain of P. pentosaceum grown on a chemically defined medium deficient in biotin. Resting cell suspensions prepared from organisms grown under these conditions were deficient in the production of carbon dioxide from added succinate, and the addition of biotin consistently more than doubled the decarboxylation rate. Hydrolysis of bound biotin yields a substance not identical with biotinic acid and exhibiting a profound stability to acid treatment. One of these complexes appears to stimulate the partially resolved decarboxylases of oxalacetate and succinate, and the deaminases of aspartic acid, serine, and threonine, thus replacing biotin in five of the enzyme systems known to be controlled by this vitamin.

Mechanism of competitive action of isonicotinic acid hydrazide and vitamin B6..

Summary On the basis of studies with apotryptophanase it is suggested that INH exerts its primary competitive effect on the vit. B6 group by competing with pyridoxal phosphate for the apoenzyme.

The role of biotin in carbohydrate metabolism of Saccharomyces cerevisiae

Abstract The investigations of the effect of biotin deficiency upon carbohydrate metabolism by washed cell suspensions of Saccharomyces cerevisiae 139 show that biotin stimulates the rate of fermentation and oxidation of carbohydrates by deficient cells. Aspartic acid partially replaces biotin in stimulating the rate of fermentation and oxidation of glucose by biotin-deficient yeast. Biotin or biotin plus aspartic acid elicits a greater response than aspartic alone in the stimulation of glucose metabolism by yeast, suggesting roles for biotin in both fermentation and oxidation other than its role in the metabolism of aspartic acid. The rate of adaptation of biotin-deficient cell suspensions of S. cerevisiae to sucrose fermentation is much more rapid in the presence of biotin, suggesting that this vitamin is concerned in the synthesis of the adaptive enzymes necessary for fermentation of this sugar. It has been found that cell-free extracts with high fermentative ability can be obtained if the synthetic medium is supplemented with 0.5% casein hydrolyzate.

Cell permeability: a factor in the biotin-oleate relationship in Lactobacillus arabinosus.

Abstract The results of this study suggest that cells of L. arabinosus are relatively impermeable to biotin. Oleic acid appears to function in permitting the more efficient entry of this vitamin into the bacterial cell.

The inhibition of malic enzyme of Lactobacillus arabinosus 17-5 by oleic acid. I. Observations on the reaction☆

Abstract The mechanism involved in the inhibition of the malic enzyme of Lactobacillus arabinosus by oleic acid has been investigated. It has been determined that the fatty acid exerts a threefold effect on the bacterial cells and the malic enzyme. It caused the dissociation of the nicotinamide-adenosine-di-nucleotide (NAD + ) co-factor from the enzyme thus rendering it unable to degrade malic acid. As a consequence of oleate treatment, malic enzyme was released from the cells. Moreover, the bacteria apparently lost their ability to maintain an internal pH different from that of the menstruum in the presence of oleic acid.

Studies in histochemistry. LVI. Microbiological determination of biotin in microgram amounts of tissue

Abstract A microbiological procedure employing Lactobacillus arabinosus for the determination of biotin in microgram quantities of tissue is described. Data pertaining to effects of various conditions of acid hydrolysis on the liberation and destruction of biotin in rat liver are presented and compared with data obtained by using Saccharomyces cerevisiae . An analysis of the reproducibility of the method is given, and data for biotin content of liver are included.

Increased Nutritional Requirements of Saccharomyces cerevisiae as a Result of Incubation at 38°C.

Summary Data were presented revealing that the paucity of growth of certain strains of yeast at 38°C is somehow related to a reduced ability to carry out the biosynthesis of pantothenic acid. Results were discussed in the light of the accepted pathway of pantothenate biosynthesis. Since the organisms are genetically endowed with the enzymic make up to synthesize pantothenate, this provides another example of the fact that environment plays an important role in genetic expression.

Inhibition of Pantothenate Synthesis by Streptomycin

Summary The results of studies on the growth response of S. fragilis to pantothenic acid and its precursors, beta-alanine and pantoyl lactone, in the presence of streptomycin, are interpreted to suggest that this antibiotic somehow interferes with the synthesis of pantothenate.

Effect of carbohydrates on aspartic acid deaminase activity of bacteria.

Summary 1. The reduction in aspartic acid deaminase activity in cells harvested from a medium containing glucose has been shown not to be specific to this sugar, but rather is shared by other fermentable carbohydrates. 2. The effect of the carbohydrate varies among the several strains studied, and is not associated with the increase in hydrogen ion concentration due to the production of fermentation acids.

The inhibition of the malic enzyme of Lactobacillus arabinosus 17-5 by oleic acid. II. Prevention of enzyme inhibition

Abstract Lecithin, Tween 40, and uranyl ions are effective in preventing oleic acid from inhibiting malic enzyme activity in whole cells of Lactobacillus arabinosus . It appears that the lecithin and Tween 40 act directly upon the fatty acid and not on the bacteria. Uranyl ions, however, apparently compete with the oleate for binding sites on the cells.