Leucine, oxidation

Figure 8.15 k plot of leucine oxidation against leucine intake. The plot illustrates a linear relab onship between leucine intake and oxidab on. The leucine intake is calculated from the protein intake. It is assumed that the same relab onship would hold for other amino acids. A similar response is seen for urea production. Data from Young et ai, 2000. 

Leucine oxidized with "OH produces a 5 -hydroperoxy derivative which is subjected to chemical reduction to yield (2S)-y-hydroxyleucine, (2S,4S)-8-hydroxy-leucine, (2S,4R)-8-hydroxyleucine. The S -hydroxyleucines have been confirmed to be the reduction products of the corresponding hydroperoxyleucines. 5 -Hydro-xylysines are natural products formed by lysyl oxidase and therefore are not useful markers of radical-mediated oxidation. The other hydroxylysines are useful markers, however, with HPLC analysis of 9-fluorenylmethyl chloroformate (FMOC)... 

Reviews by Ruderman (19) and Adibi (20,21) indicate that the branched-chain amino acids, particularly leucine, have an important role along with alanine in gluconeogenesis. Leucine and the other two branched-chain amino acids are catabolized in skeletal muscle. The nitrogen that is removed from the branched-chain amino acids in skeletal muscle is combined with pyruvate and returned to the liver as alanine. In the liver the nitrogen is removed for urea production and the carbon chain is utilized as substrate for synthesis of glucose. Adibi et al. (22) reported that during the catabolic conditions of starvation, oxidation of leucine and fatty acids increases in skeletal muscles. While glucose oxidation is reduced, the capacity for oxidation of the fatty acid palmltate more than doubled, and leucine oxidation increased by a factor of six. 

The mechanism that produces increased amino acid oxidation during exercise is unknown. White and Brooks (29) demonstrated a relationship of amino acid oxidation to use oT blood glucose. Concomitant with increases in the intensity of exercise and leucine oxidation, the oxidation of glucose and alanine increased. These data in combination with the earlier reports of increased flux of leucine to skeletal muscles and alanine from muscles to the liver suggest that the oxidation of amino acids may be linked to the need for glucose and to generation of substrates for gluconeogenesis. 

The work by Wolfe et al. (31,32) serves to emphasize some of these problems. They utilized a mild bicycle exercise and examined the effects on leucine oxidation and urea production. 

Preliminary work in our laboratory suggests that the effect of exercise on leucine oxidation is not just a transient effect of beginning an exercise program, and that the magnitude of the effect is dependent on the duration of the exercise (Fig. 2). 

The curves in Figure 2 indicate that exercise increases leucine oxidation and that the stimulation may be directly related to duration of exercise. 

Paul, H.S., and S.A. Adibi. 1980. Leucine oxidation and protein turnover in clofibrate-induced muscle protein degradation in rats. 65 1285-93. 

Branched-chain monoarainomono-carboxylic acids Valine > isoleucine > leucine Only leucine oxidized Leucine > isoleucine > valine Leucine > isoleucine, valine Only leucine oxidized... 

In contrast to endurance exercise, acute whole-body resistance exercise does not alter leucine oxidation. In this same study we also did not find an effect of acute resistance exercise on whole-body protein synthesis, either during exerdse or for up to 2 h post-exerdse. We hypothesized that since muscle protein synthesis (MPS) accounted for only 25% of whole-body synthesis, changes in MPS either may be not measurable or would be negated by a redprocal change in the synthesis of another protein, such as one in the gastrointestinal tract. 

There is no question that dehydration can significantly alter exercise performance and ultimately lead to more severe medical disorders such as heat stress and heat stroke. Hydration status is also a determinant of amino acid oxidation, with cellular dehydration inducing an increase in leucine oxidation and cellular hyperhydration showing the opposite in resting yoimg men.Although dehydration dining... 

McKenzie, S., Phillips, S.M., Carter, S.L., Lowther, S., Gibala, M.J., and Tarnopolsky, M.A., Endurance exercise training attenuates leucine oxidation and BCOAD activation during exercise in humans. Am J Physiol Endocrinol Metab, 278, E580, 2000. 

El-Khoury, A.E., Forslund, A., Olsson, R. et al.. Moderate exercise at energy balance does not affect 24-h leucine oxidation or nitrogen retention in healthy men. Am J... 

Gaine, FC., Viesselman, C.T., Pikosky, M.A. et al.. Aerobic exercise training decreases leucine oxidation at rest in healthy adults, J Nutr, 135, 1088, 2005. Campbell, W.W., Crim, M.C., Young, V.R., Joseph, L.J., and Evans, W.J., Effects of resistance training and dietary protein intake on protein metabolism in older adults. Am J Physiol, 268, El 143, 1995. 

Note numbers between [] at the end of a reference designate the literature used for the sub-database of that number. Bequette, B.J., F.R.C. Baokwell, J.C. MacRae, G.E. Lobley, L.A. Crompton, J.A. Metcalf, and J.D. Sutton, 1996. Effect of intravenous amino acid infusion on leucine oxidation across the mammary gland of the lactating goat. 

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