Vitamin fatty acid metabolism

The number of vitamin B 12-dependent reactions is not large. Most of these involve rearrangements of the carbon skeletons of metabolites. Such reactions are important in linking some aspects of fatty acid metabolism to the citric acid cycle. In another form, a vitamin Bi2-derived coenzyme is involved, along with folic acid coenzymes, in the metabolism of one-carbon fragments, including the biosynthesis of methionine. 

Vitamin Bj (8.44, riboflavin) is a benzopteridine derivative carrying a ribityl (reduced ribose) side chain. It occurs in almost all foods, the largest amounts being found in eggs, meat, spinach, liver, yeast, and milk. Riboflavin is one of the major electron carriers as a component of flavine-adenine dinucleotide (FAD), which is involved in carbohydrate and fatty acid metabolism. A hydride ion and a proton are added to the pyrazine ring of... 

Cyanocobalamin A cofactor required for essential enzymatic reactions that form tetrahydrofolate, convert homocysteine to methionine, and metabolize l-methylmalonyl-CoA Adequate supplies are required for amino acid and fatty acid metabolism, and DNA synthesis Treatment of vitamin B12 deficiency, which manifests as megaloblastic anemia and is the basis of pernicious anemia Parenteral vitamin B12 is required for pernicious anemia and other malabsorption syndromes Toxicity No toxicity associated with excess vitamin B12... 

Vitamin B12 (cyancobali-min, cobalamin) Protein and fatty acid metabolism production of red blood cells maintenance of nervous system, concentration and memory. Clams, oysters, beef, eggs and dairy products. Not found in many plant products strict vegetarians may need to consider Bi2 supplements. 2 mg No... 

Description. Also known as vitamin Bg or H, this vitamin is of great importance for the biochemistry of the human organism. Biotin is the cofactor for a small group of enzymes that catalyze carboxyla-tion, decarboxylation, and transcarboxylation reactions in carbohydrate and fatty acid metabolism. Deficiency of this vitamin is rare in humans, but can be induced in special circumstances in individuals with inborn errors of biotin metabolism, in individuals taking certain medications, and in some women during pregnancy. ... 

CoA Coenzyme A, a B-vitamin-derived cofactor essential for fatty acid metabolism, pyruvate oxidation, TCA cycle, etc. 

All aspects of the biochemical role of biotin have not yet been clarified. The vitamin has been implicated in the metabolism of carbohydrates, lipids, proteins, and nucleic acids. Available evidence indicates that biotin acts as a CO2 carrier in a number of carboxyla-tion and decarboxylation reactions connected with carbohydrate and fatty acid metabolism. A number of experimental procedures are used to establish the participation of biotin in a given biochemical reaction (1) the study of enzyme activity in biotin-deficient animals (2) the effect of avidin administered in vivo or added to the incubation mixture on the activity of the enzyme under study and (3) purification of the enzyme and demonstration of the existence of enzyme-bound biotin. Studies of this kind have established that biotin is required for the carboxylases of jS-methyl-crotonyl CoA, acetyl-CoA, propionyl CoA, and oxaloacetic transcarboxylase. Only some of the results are presented here [74-76]. 

In the tissues, vitamin Be occurs predominantly as the phosphate of pyridoxal or pyridoxamine, especially the former, except in the liver. Pyri-doxal phosphate functions as a coenzyme in four types of reactions decarboxylation of amino acids, transamination, and the synthesis and cleavage of tryptophan (Chapter 19). This coenzyme is necessary for the deamination of amino acids and for the formation of urea nitrogen. It appears to be essential for the conversion of tryptophan to the pyridine coenzymes. Pyridoxine may be related to fatty acid metabolism and seems to be necessary for normal adrenal cortical function. ... 

Table 2 Vitamins associated with fatty-acid metabolism ...

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. 

The 4-phosphopantetheine group of CoA is also utilized (for essentially the same purposes) in acyl carrier proteins (ACPs) involved in fatty acid biosynthesis (see Chapter 25). In acyl carrier proteins, the 4-phosphopantetheine is covalently linked to a serine hydroxyl group. Pantothenic acid is an essential factor for the metabolism of fat, protein, and carbohydrates in the tricarboxylic acid cycle and other pathways. In view of its universal importance in metabolism, it is surprising that pantothenic acid deficiencies are not a more serious problem in humans, but this vitamin is abundant in almost all foods, so that deficiencies are rarely observed. 

What would be the consequences of a deficiency in vitamin Bi2 for fatty acid oxidation What metabolic intermediates might accumulate ... 

Besides water, the diet must provide metabolic fuels (mainly carbohydrates and lipids), protein (for growth and turnover of tissue proteins), fiber (for roughage), minerals (elements with specific metabolic functions), and vitamins and essential fatty acids (organic compounds needed in small amounts for essential metabolic and physiologic functions). The polysaccharides, tri-acylglycerols, and proteins that make up the bulk of the diet must be hydrolyzed to their constituent monosaccharides, fatty acids, and amino acids, respectively, before absorption and utilization. Minerals and vitamins must be released from the complex matrix of food before they can be absorbed and utifized. 

Besides watet, the diet must provide metaboEc fuels (carbohydrate and fat) fot bodily growth and activity protein fot synthesis of tissue proteins fiber for roughage minerals for specific metabolic functions cettain polyunsamtated fatty acids of the n-3 and n-6 famihes fot eicosanoid synthesis and other functions and vitamins, otganic compounds needed in small amounts for many varied essential functions. 

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