Methionine, Iodocasein and Oxygen Consumption of Chicks

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Abstract
A factorial design, using vitamin B12, DL-methionine and iodocasein with a vitamin B12 deficient, methionine-deficient basal diet, has been used to compare the effects of these supplements on oxygen consumption and amino acid utilization in chicks. The basal diet was balanced with respect to essential amino acids except for methionine, grossly deficient, and histidine and isoleucine, which were in excess. Iodocasein decreased growth and feed efficiency, increased oxygen consumption of the intact animals, and also the weight of their livers compared to body weight. Methionine reversed all of these effects of iodocasein. Further, methionine in the absence of iodocasein had effects on the foregoing criteria opposite from those of iodocasein. Since thyroid hormone is a metabolic uncoupler it is suggested that methionine functions in metabolism as a coupling agent or by enhancing biosynthesis of such an agent, or by interfering otherwise with the functioning of the thyroid hormone as an uncoupler. Thus methionine may be a factor in linking anabolic reactions to oxidative reactions, thereby making available the energy provided by the latter for more effective animal function. And thus there is here a possible basic explanation of the results of its deficiency. Methionine, and to some extent vitamin B12, reduced excretion of uric acid from that found in controls. In the case of methionine this was concomitant with an obvious correction of methionine deficiency. Hence the reduction of uric acid excretion by vitamin B12 in the absence of added methionine suggests that the vitamin also corrected the amino acid imbalance to some extent. This is consistent with the findings that vitamin B12, like methionine but to a lesser degree, also improved growth and feed utilization efficiency, and reduced liver size.