A COMPARATIVE STUDY OF THE REGULATION OF PYRIDINE NUCLEOTIDE FORMATION

Enhancement of tacrolimus productivity in Streptomyces tsukubaensis by the use of novel precursors for biosynthesis

In this report the optimization of biosynthesis of tacrolimus, the immunosupressant widely used in transplantology and dermatology was described. The enhancement of the productivity of Streptomyces tsukubaensis strain was achieved by development of new precursors of tacrolimus biosynthesis, which should allow to reduce the costs of the process. The enrichment of the fermentation medium in pyridine-2-carboxylic acid (picolinic acid), piperidine-2-carboxylic acid (pipecolic acid), pyridine-3-carboxylic acid (nicotinic acid) or pyridine-3-carboxylic acid amide (nicotinamide) caused significant growth of the productivity of tacrolimus: 7-fold, 6-fold, 3-fold and 5-fold, respectively. The optimum concentration of the precursors in medium was 0.0025-0.005%. The investigation of the kinetics of tacrolimus biosynthesis together with the analysis of the impact of tested compounds on the culture growth and NAD (nicotinamide adenine dinucleotide) concentration in S. tsukubaensis cells enables to put forward a hypothesis concerning the mechanism of action of tested culture medium additives. The compounds active as tacrolimus precursors (pipecolic and picolinic acids) are more effective than these active mainly as the growth promoters (nicotinamide and nicotinic acid). Nicotinamide and nicotinic acid--vitamin B₃ components--promote S. tsukubaensis growth most probably due to the stimulation of NAD/NADP biosynthesis.

Effect of leucine on enzymes of the tryptophan-niacin metabolic pathway in rat liver and kidney

Dietary excess of leucine affects tryptophan-niacin metabolism adversely and has thus been implicated in the etiology of pellagra. To understand the biochemical basis of leucine-induced changes in tryptophan-niacin metabolism the effect of leucine on enzymes of tryptophan-niacin metabolism was investigated. Excess of leucine in the diet had no effect on rat liver 3-hydroxyanthranilate oxygenase and nicotinate phosphoribosyltransferase but significantly decreased the activity of quinolinate phosphoribosyltransferase of rat liver and kidney. The activities of tryptophan oxygenase in liver and picolinate carboxylase in kidney were significantly higher in leucine-fed animals than in the controls. Also, oxidation of [U-(14)C]tryptophan in vivo was higher in leucine-fed animals. Increased picolinate carboxylase and decreased quinolinate phosphoribosyltransferase activities would result in a decrease in NAD formation from dietary tryptophan. Lowered NAD formation from tryptophan particularly when the niacin concentrations in the diet are marginal would result in a state of conditioned niacin deficiency.

Enzymology of NAD+ synthesis

Beyond its role as an essential coenzyme in numerous oxidoreductase reactions as well as respiration, there is growing recognition that NAD+ fulfills many other vital regulatory functions both as a substrate and as an allosteric effector. This review describes the enzymes involved in pyridine nucleotide metabolism, starting with a detailed consideration of the anaerobic and aerobic pathways leading to quinolinate, a key precursor of NAD+. Conversion of quinolinate and 5'-phosphoribosyl-1'-pyrophosphate to NAD+ and diphosphate by phosphoribosyltransferase is then explored before proceeding to a discussion the molecular and kinetic properties of NMN adenylytransferase. The salient features of NAD+ synthetase as well as NAD+ kinase are likewise presented. The remainder of the review encompasses the metabolic steps devoted to (a) the salvaging of various niacin derivatives, including the roles played by NAD+ and NADH pyrophosphatases, nicotinamide deamidase, and NMN deamidase, and (b) utilization of niacins by nicotinate phosphoribosyltransferase and nicotinamide phosphoribosyltransferase.

Identification of a cis-acting regulatory region in the pncB locus of Salmonella typhimurium

The pncB locus of the pyridine nucleotide cycle of NAD biosynthesis in Salmonella typhimurium was examined in terms of genetic structure and regulation. The gene appears to be regulated at the level of transcription in response to the end product of the pathway, NAD. Insertions into promotor proximal regions of the gene relinquish it from regulation, while insertions into more distal regions allow retention of regulation. Regulation cannot be restored in trans to strains containing promotor proximal insertions implicating the existence of a cis acting regulatory region.

Structural features of the phosphoribosyltransferases and their relationship to the human deficiency disorders of purine and pyrimidine metabolism

Similarities in the physical and chemical properties of the phosphoribosyltransferase family of enzymes suggest that they may share common structural features as observed in other functionally related proteins. The unusually high incidence of structural gene mutations of these enzymes in man are associated with several metabolic diseases of purine and pyrimidine metabolism. It is proposed that these disorders are the consequence of structural mutations to an architectural domain common to all of the phosphoribosyltransferases.

Pyridine nucleotide cycle of Salmonella typhimurium: isolation and characterization of pncA, pncB, and pncC mutants and utilization of exogenous nicotinamide adenine dinucleotide

Mutants of Salmonella typhimurium LT-2 deficient in nicotinamidase activity (pncA) or nicotinic acid phosphoribosyltransferase activity (pncB) were isolated as resistant to analogs of nicotinic acid and nicotinamide. Information obtained from interrupted mating experiments placed the pncA gene at 27 units and the pncB gene at 25 units on the S. typhimurium LT-2 linkage map. A major difference in the location of the pncA gene was found between the S. typhimurium and Escherichia coli linkage maps. The pncA gene is located in a region in which there is a major inversion of the gene order in S. typhimurium as compared to that in E. coli. Growth experiments using double mutants blocked in the de novo pathway to nicotinamide adenine dinucleotide (NAD) (nad) and in the pyridine nucleotide cycle (pnc) at either the pncA or pncB locus, or both, have provided evidence for the existence of an alternate recycling pathway in this organism. Mutants lacking this alternate cycle, pncC, have been isolated and mapped via cotransduction at 0 units. Utilization of exogenous NAD was examined through the use of [14C]carbonyl-labeled NAD and [14C]adenine-labeled NAD. The results of these experiments suggest that NAD is degraded to nicotinamide mononucleotide at the cell surface. A portion of this extracellular nicotinamide mononucleotide is then transported across the cell membrane by nicotinamide mononucleotide glycohydrolase and degraded to nicotinamide in the process. The remaining nicotinamide mononucleotide accumulates extracellularly and will support the growth of nadA pncB mutants which cannot utilize the nicotinamide resulting from the major pathway of NAD degradation. A model is presented for the utilization of exogenous NAD by S. typhimurium LT-2.

Inhibition by phenylalanine of thiazole biosynthesis in Escherichia coli

Phenylalanine inhibited thiazole biosynthesis in a thiamine-regulatory mutant of Escherichia coli, and the inhibition was overcome by tyrosine.

Pathway-specific pattern of control of arginine biosynthesis in bacteria

Udaka, Shigezo (The Institute of Physical and Chemical Research, Komagome, Bunkyo-ku, Tokyo, Japan). Pathway-specific pattern of control of arginine biosynthesis in bacteria. J. Bacteriol. 91:617-621. 1966.-To compare control mechanisms of arginine biosynthesis in various bacteria, activities of several enzymes of the arginine pathway were measured in cells cultivated under repressed and partially derepressed conditions. Nineteen strains of bacteria tested appeared to have two types of pathways, closely related to each other. The partially derepressed levels of enzymes varied from bacterium to bacterium. The degree of inhibition of enzyme 2 (the second of eight enzymes concerned with arginine biosynthesis) and the repressibility of enzymes by arginine also appeared to vary from species to species. On the other hand, enzyme 2 was found to be the site of end-product inhibition only in the bacteria having a particular pathway. These results suggest that the bacteria have their own species-specific control mechanisms and that there is a pathway-specific pattern of control in arginine biosynthesis. The implications of the results are discussed from the viewpoint of evolution of control mechanisms.