Nonprotein Amino Acids

There are several amino acids found in biological systems that are not incorporated into proteins. Ornithine and citrulline, for example, are intermediates of the urea cycle; GABA is a neurotransmitter.

Homocysteine is an intermediate in the transul-phuration pathway for the conversion of methio-nine to cysteine. Homocystinuria is an inborn error of metabolism that is characterized by the accumulation of high concentrations of homocys-teine, and this leads to severe cardiovascular disease at an early age. However, there is a much more common mutation in the enzyme 5,10-methylenetetrahydrofolate reductase that causes a moderate increase in plasma homocysteine concentration in more than 10% of the population. A high plasma homocysteine concentration appears to be an independent risk factor for cardiovascular disease in the population as a whole, although the mechanism is not known. Supplementing the diet with folic acid is often effective in reducing plasma homocysteine concentration because methyltetra-hydrofolate is a substrate for the remethylation of homocysteine by the vitamin B12-dependent enzyme methionine synthase. An inverse relationship has been observed between plasma homocys-teine concentration and folate status in many studies, and this has led to the proposal that plasma homocysteine concentration may be used as a biomarker of folate intake.

Gaining Weight 101

Gaining Weight 101

Find out why long exhausting workouts may do more harm than good. Most of the body-building workout and diet regimens out there are designed for the guys that gain muscle and fat easily. They focus on eating less and working out more in order to cut the excess fat from their bodies while adding needed muscle tone.

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