Glucose, biotin vitamin

To replace losses, oxaloacetate can be synthesized from pyruvate and C02 in a reaction that uses ATP as an energy source. This is indicated by the heavy gray line leading downward to the right from pyruvate in Fig. 10-1 and at the top center of Fig. 10-6. This reaction depends upon yet another coenzyme, a bound form of the vitamin biotin. Pyruvate is formed from breakdown of carbohydrates such as glucose, and the need for oxaloacetate in the citric acid cycle makes the oxidation of fats in the human body dependent on the concurrent metabolism of carbohydrates. 

Potato extract, orange juice and yeast extract all stimulate the fermentation of glucose and acid production by propionic acid bacteria (Tatum et al., 1936). Stimulation by potato extract is associated with some essential growth factors. If synthetic medium is supplemented with yeast extract, then the addition of individual vitamins (biotin, pantothenate, thiamine or /7-aminobenzoic acid) is unnecessary (El-Hagarawy, 1957). In connection with the ability of P. shermanii to synthesize vitamins Karlin (1966) suggested to include these bacteria into dairy products. For example, kefir enriched with P. shermanii contained increased amounts of vitamin Bi, B2, Bg, PP, Bi2, pantothenate, folic and folinic acid as compared with control samples. Especially high increases in the latter four vitamins were observed. 

Pyruvate is converted to phosphoenolpyruvate for glucose synthesis by a two-step reaction, with the intermediate formation of oxaloacetate. As shown in Figure 5.31, pyruvate is carboxylated to oxaloacetate in an ATP-dependent reaction in which the vitamin biotin (section 11.12) is the coenzyme. This reaction can also be used to replenish oxaloacetate in the citric acid cycle when intermediates have been withdrawn for use in other pathways, and is involved in the return of oxaloacetate from the cytosol to the mitochondrion in fatty acid synthesis — see Figure 5.26. Oxaloacetate then undergoes a phosphorylation reaction, in which it also loses carbon dioxide, to form phosphoenolpyruvate. The phosphate donor for this reaction is GTP as discussed in section 5.4.4, this provides regulation over the use of oxaloacetate for gluconeogenesis if citric acid cycle activity would be impaired. 

A considerable amount of biotin is synthesized by human intestinal bacteria, as evidenced by the fact that 3 to 6 times more biotin is excreted in the urine and feces than is ingested. But synthesis in the gut may occur too late in the intestinal passage to be absorbed well and play much of a direct role as a biotin source. Also, several variables affect the microbial synthesis in the intestines, including the carbohydrate source of the diet (starch, glucose, sucrose, etc.), the presence of other B vitamins, and the presence or absence of antimicrobial drugs and antibiotics. 

Furthermore, adequate minerals and vitamins must Ere available for the proper metabolism of glucose. Minerals are cofactors with many of the enzymes involved, and with the B complex vitamins—thiamin, niacin, ribroflavin, pantothenic acid, vitamin B-6, biotin, and folacin. 

For better control of fermentation and to reduce production costs, complex media components are avoided and mostly refined carbon sources are used for the industrial production of L-lysine. Sucrose can be obtained from cane or beet molasses, and glucose is provided in hydrolysates of corn, cassava, or wheat starch [30, 83]. Ammonia, as nitrogen source, can be added pure or as salts [32]. Further media components are vitamins, in particular biotin, as well as salts and trace elements. Amino acids for auxotrophic production strains can be provided by peptones, corn steep liquors, or soybean meal hydrolysates [30]. Preferably, media are sterilized continuously, whereas carbon sources and nitrogen sources are typically sterilized separately to avoid Maillard-type reactions [32]. Sterility is important for processes with the mesophilic and neutrophilic C. glutamicum with bacilli as main contamination risk [84], while phage infection is hardly a problem. 

Several of the B vitamins are essential for normal fatty-acid metabolism (Table 2). Pantothenic acid is a constituent of CoA and is thus required for numerous reactions of fatty acids. Niacin and riboflavin are necessary for the synthesis of oxidized and reduced NAD(P) and FAD, respectively. These compounds play essential roles in fatty-acid oxidation, synthesis, and elongation. Biotin is a constituent of acetyl-CoA carboxylase and pyruvate carboxylase, both of which are involved in the synthesis of fatty acids from glucose. Thiamine is required for activity of the pyruvate dehydrogenase complex, which also participates in fatty-acid synthesis from glucose. 

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