Leucine turnover

Bowtell, J.L., Leese, G.P., Smith, K. et al.. Effect of oral glucose on leucine turnover in human subjects at rest and during exercise at two levels of dietary protein, J Physiol, 525 (Pt 1), 271, 2000. 

Extrapolating from leucine turnover studies in pigs, it is estimated that endogenous HMB production is equal to 0.2 to 0.4 g of HMB/day in a 70-kg man, depending on leucine intake. Furthramore, turnover of HMB is thought to be relatively rapid, as basal plasma concentrations in normal humans range from 1 to 4 Plasma levels of... 

These three compounds exert many similar effects in nucleotide metabolism of chicks and rats [167]. They cause an increase of the liver RNA content and of the nucleotide content of the acid-soluble fraction in chicks [168], as well as an increase in rate of turnover of these polynucleotide structures [169,170]. Further experiments in chicks indicate that orotic acid, vitamin B12 and methionine exert a certain action on the activity of liver deoxyribonuclease, but have no effect on ribonuclease. Their effect is believed to be on the biosynthetic process rather than on catabolism [171]. Both orotic acid and vitamin Bu increase the levels of dihydrofolate reductase (EC 1.5.1.4), formyltetrahydrofolate synthetase and serine hydroxymethyl transferase in the chicken liver when added in diet. It is believed that orotic acid may act directly on the enzymes involved in the synthesis and interconversion of one-carbon folic acid derivatives [172]. The protein incorporation of serine, but not of leucine or methionine, is increased in the presence of either orotic acid or vitamin B12 [173]. In addition, these two compounds also exert a similar effect on the increased formate incorporation into the RNA of liver cell fractions in chicks [174—176]. It is therefore postulated that there may be a common role of orotic acid and vitamin Bj2 at the level of the transcription process in m-RNA biosynthesis [174—176]. 

The biosynthetic incorporation of amino acids into proteins makes these metabolites valuable endogenous tracers for the characterization of protein turnover. Of the naturally occurring amino acids, administration of a bolus dose of pH]leucine is widely used as a tracer in kinetic investigations of protein synthesis and secretion. 

BRANCHED-CHAIN AMINO ACID AMINOTRANSFERASE LEUCINE DEHYDROGENASE LEUCINE KINETICS RROTEIN TURNOVER KINETICS SAAM... 

NUCLEAR MAGNETIC RESONANCE PROTEIN SYNTHESIS INHIBITORS PROTEIN TURNOVER N-END RULE LEUCINE KINETICS PROTEASE La... 

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. 

Binuclear zinc complexes have been shown to mediate the hydrolysis of the activated peptide model substrate L-leucine- -nitroanilide (LNA, Fig. 32) with the reactions being followed spectroscopically by the formation of /7-nitroaniline ( max 400 nm).165-167 This model substrate has also been used in studies of ApAP.170 The hydrolysis of LNA mediated by the zinc complex [(bomp-)]Zn2(CH3C02)2]BPh4 (Fig. 33a H(bomp) 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-methylphenol) in water/DMF (6 4) occurs via a reaction that is first-order in complex and substrate, with a second-order rate constant k = 2.3(1) x 10 3M 1 s-1 at 25 °C. At best, a yield of 65% for a single turnover reaction was obtained, indicating that... 

From studies on the incorporation of [3H]-leucine into proteins of the synaptic vesicles and nerve ending membranes, a half life of 20-22 days was calculated (Von Hungen et al., 1968). Lapetina et al. (1969) found a more rapid turnover for brain phospholipids, though different parts of the molecule seemed to turn over at different rates. Acylation of lysophospholipids to diacyl-phospholipids seems to be carried... 

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

Similar studies are conducted using C-enriched triglycerides to study fatty acid metabolism, again following the expiration of 2. Protein turnover has been studied by administering N-enriched amino acids and measuring enrichment in excreted urea. C-leucine has also been used but on this occasion C02 enrichment in expired air was followed. 

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