Metabolic rate, riboflavin

Although there is no evidence that patients treated with these drugs for a prolonged period develop clinical signs of riboflavin deficiency, long-term use of chlorpromazine is associated with a reduction in metabolic rate. 

The main metabolic effect of riboflavin deficiency is on lipid metabolism. Riboflavin-deficient animals have a lower metabolic rate than controls, and require a 15—20% higher food intake to maintain body weight. Feeding a high-fat diet leads to more marked impairment of growth and a higher requirement for riboflavin to restore growth. 

Many factors affect folate metabolism, including dietary folate level, nutritional status of vitamins B6, B12, and riboflavin, zinc status, alcoholism, and physical states such as pregnancy and lactation. In many cases, the effects of these factors are seen in altered excretion rates of intact folates and metabolites, but the effects on tissue levels of the various folates and transfer rates between tissues are not well understood. Preliminary human and animal kinetic models are being devek ed in our laboratory based on studies conducted under controlled dietary conditions. These models will provide a base from which to study the effects of altered folate nutriture as well as the influence of other factors such as pregnancy and aging on folate metabolism. 

Goodwin and Jones (75) uang E. aahbyii found that the addition of unlabeled adenine markedly depressed the incorporation of label from serine-C into riboflavin, but had no effect on the amount of serine-C metabolized to carbon dioxide. This might indicate that a purine is an obligatory intermediate. However, the results could be explained equally well by the second scheme, if the rate of convermon of purines to rings B and C is more rapid than the rate of synthesis from the simple precursors, or if the added purine inhibits one of the steps of the de novo formation of riboflavin. 

Because of the slow rate of flavin synthesis by the crude enzyme system, it has been difficult to determine the origin of the four-cari)on unit which condenses with 6,7-dimethyl-8-ribityllumazine to yield the o-xylene ring of the flavin. Two possibilities are apparent, either of which is conristent with the data obtained with radioactive glucose (86) (see Table III and Fig. 4). (a) Acetoin and diacetyl arise from pyruvate in metabolic qrstems and either one will condense chemically with 6,7-dimethyl-8-ribitylluma-zine to yield riboflavin. However, addition of diacetyl to the enzyme system from A. gosaypii did not enhance the incorporation of label from 6,7-... 

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