Leucine oxidation, effect

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). 

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. 

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. 

An entirely different property of subtilisin was affected by substituting leucine at the 222 location. Native BPN is extremely sensitive to the presence of oxidation agents, showing rapid inactivation when incubated in the presence of 0.3% H2O2 (Figure 4). The Leu-222 variant, in contrast, was found to be totally stable under the same oxidation conditions. The data clearly show that single amino acid alterations can have dramatic effects upon the activity of the enzyme. Similarly, other changes have been shown to affect catalytic properties, substrate specificities and thermostability (7,2,9). 

An elegant four-enzyme cascade process was described by Nakajima et al. [28] for the deracemization of an a-amino acid (Scheme 6.13). It involved amine oxidase-catalyzed, (i )-selective oxidation of the amino acid to afford the ammonium salt of the a-keto acid and the unreacted (S)-enantiomer of the substrate. The keto acid then undergoes reductive amination, catalyzed by leucine dehydrogenase, to afford the (S)-amino acid. NADH cofactor regeneration is achieved with formate/FDH. The overall process affords the (S)-enantiomer in 95% yield and 99% e.e. from racemic starting material, formate and molecular oxygen, and the help of three enzymes in concert. A fourth enzyme, catalase, is added to decompose the hydrogen peroxide formed in the first step which otherwise would have a detrimental effect on the enzymes. 

Valine.—This amino acid is contained mixed with leucine in the fractions of the esters which boil between 6o° and 90° C. Its isolation and separation from leucine is of extreme difficulty, since these compounds, as well as their copper salts into which they are converted by boiling with freshly precipitated cupric oxide, tend to form mixed crystals. Its isolation was only effected by these means in certain cases, and its amount is really much more than the figures represent from its yield. It is best characterised by conversion into its phenylhy-dantoine derivative by treatment with phenyl isocyanate in alkaline solution. The phenylureido acid is first formed, and this loses a molecule of water, as shown by Mouneyrat, and is changed into its anhydride or phenylhydantoine by treatment with hydrochloric acid. The following reactions occur —... 

Four untrained men were exercised for 105 minutes on a bicycle ergometer at an intensity designed to maintain a heart rate of 110 beats/minute (approximately 30% V02niax Comparing a pre-exercise rest period to immediately post-exercise, they found a 2- to 3-fold increase in the production of CO2 from leucine, but they found no Increase in urea production. They also determined that while mild exercise Increased oxidation of leucine, there was no effect on the catabolism of another essential amino... 

Aerobic exercise usually increases the percentage of muscle mass due to a decrease in body fat, but produces no absolute change in the amount of muscle. Aerobic exercise has been shown to alter protein metabolism including increases in amino acid oxidation with specific effects on the branched-chain amino acid leucine, increased urinary urea, and increased sweat nitrogen. 

Hogg, S.A., Morse, E.L. Adibi, S.A. (1982) Effect of exercise on rates of oxidation, turnover, and plasma clearance of leucine in human subjects. Amer. J. Physiol. 242, E407-E410. 

Sabine, represent spontaneous mutations. The effect of the substitution can be extremely mild (Hb-Richmond, Hb-I-Toulouse) to severe (Hb-Bibba, Hb-Hammersmith). Subjects with Hb-Zurich are asymptomatic unless exposed to oxidant drugs causing an acute hemolytic episode with formation of Heinz bodies. Particularly severe is the lesion in Hb-Hammersmith because the removal of phenylalanine GDI is accompanied by the introduction of the polar OH group of serine which probably facilitates the entry of water into the heme pocket which causes the heme group to drop out (P14). Substitution of this phenylalanine by leucine, as in Hb-Louisville, results in a much less severe anemia (K9). 

Previously, we have examined the formation of amino acid hydroperoxides following exposure to different radical species [100]. We observed that valine was most easily oxidised, but leucine and lysine are also prone to this modification in free solution. Scheme 12 illustrates the mechanism for formation of valine hydroperoxide. However, tertiary structure becomes an important predictor in proteins, where the hydrophobic residues are protected from bulk aqueous radicals, and lysine hydroperoxides are most readily oxidised. Hydroperoxide yield is poor from Fenton-derived oxidants as they are rapidly broken down in the presence of metal ions [101]. Like methionine sulphoxide, hydroperoxides are also subject to repair, in this case via glutathione peroxidase. They can also be effectively reduced to hydroxides, a reaction supported by the addition of hydroxyl radical in the presence of oxygen. Extensive characterisation of the three isomeric forms of valine and leucine hydroxides has been undertaken by Fu et al. [102,103], and therefore will not be discussed further here. 

All amino acids are not affected to the same extent. Bergel and Bolz28 found that leucine is oxidized ten times faster than alanine. Fiirth29 reports that histidine and proline are relatively stable, and Wunderly30 finds that the deaminating effect is specific for the true amino grouping. 

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