Compartmentation of free amino acids for protein synthesis in rat liver

The concept that a general intracellular pool serves as the sole precursor of amino acids for protein biosynthesis has been vigorously debated in recent years. To help resolve this controversy, we followed the distribution of intraperitoneally administered [(3)H]valine in the tRNA and the extracellular and intracellular compartments of rat liver. The specific radioactivity of the valine released from isolated tRNA was 2-3 times higher than that of intracellular valine, suggesting that the intracellular pool cannot be the sole precursor of amino acids used for charging tRNA. In addition, the specific radioactivity of the tRNA was only half that of the extracellular valine. Therefore it is unlikely that the valyl-tRNA is charged exclusively with amino acids derived from the extracellular pool. A model is proposed which stipulates that both extracellular and intracellular amino acids contribute to a restricted compartment that funnels amino acids towards protein biosynthesis.     

Changes in free and bound amino acids in experimental silicosis.

The amino acid composition of lung, serum and liver in silicotic rats was studied in order to assess the availability of precursors in lung for fibrogenesis. It was observed that the pool of ornithine, arginine, alanine, leucine, valine, glutamic acid, lysine, proline and glycine underwent marked alterations. Free arginine, proline and leucine were only detectable in silicotic lung, while free glycine, glutamic acid and glutamine pools decreased significantly in liver. Changes in amino acid metabolism as a result of silicosis are discussed.     

Protein synthesis: twenty three amino acids and counting

The genetic code can be interpreted during translation as 21 amino acids and three termination signals. Recent advances at the interface of chemistry and molecular biology are extending the genetic code to allow assignment of new amino acids to existing codons, providing new functional groups for protein synthesis.     

Protein and free amino acids in a high lysine maize double mutant

A comparative study of free amino acids and protein fractions of normal with a double mutant (su₁ o₂) was made, during endosperm development in segregating ears of a maize synthetic. Zein content showed striking differences in the two genotypes, being 7.7 and 6 times greater in the normal endosperm at 24 and 47 days after pollination respectively. This observed decrease in zein synthesis, coded by sugary-1/opaque-2 genes, causes an accumulation of alanine, glutamic and aspartic acids, glutamine and asparagine in the high lysine endosperm mutant.     

The effects of melatonin and L-DOPA on the diurnal rhythms of free amino acids content in the rat retina

The effects of melatonin and dopamine precursor L-3,4-dihydroxyphenylalanine (L-DOPA) intraperitoneal administration on the rhythms of free amino acids content in the retina of rats were studied. The authors found that the levels of those amino acids, which are protein constituents but not neurotransmitters in the rat retina, change diurnally with maximum at 3-6 h after light onset. Diurnal changes of Ala, Arg, Asn, Ile, Met, Ser, Trp, and Val content persisted in the retina of rats maintained at constant darkness. This fact confirms the true circadian nature of these rhythms. Constant lighting abolished diurnal changes of the content of all amino acids with the exception of Trp. Daytime but not nighttime administration of melatonin decreased the levels of Ala, Asn, Gln, Ile, Met, and Ser down to nocturnal values. Diurnal changes of amino acids content vanished in melatonin-injected rats. The effect of melatonin administration disappeared when the protein synthesis was inhibited by cycloheximide. The effect of intraperitoneal administration of L-DOPA on the levels of free amino acids was opposite the effect of melatonin administration. L-DOPA increased nocturnal levels of Gly, Thr, Trp, and Val but had no effect on the daytime amino acids content. As in the case of melatonin administration, significant diurnal changes of amino acid levels disappeared in L-DOPA-injected rats. The authors hypothesize that melatonin and dopamine can serve as zeitgebers-antagonists of amino acids content rhythms in the rat retina.     

Dynamics of free amino acids in rat brain tissue during hypothermia

A comparative study is conducted for the effect of one-, three- and six-hour artificial deep (20-19 degrees C) hypothermia on the content of free amino acids in the blood serum, tissue, nuclei and mitochondria of the rat brain. It is found out that the content is the highest in the blood serum after a three-hour cooling. In the brain tissue the amount of amino acids lowers, especially under conditions of a six-hour hypothermia. In nuclei a three-hour effect of hypothermia decreases sharply the content of free amino acids and the six-hour one increases the amount of most of them. Under hypothermia the content of nearly all amino acids in the brain mitochondria is higher than in the intact animals.     

Effect of fluchloralin on protein synthesis, free amino acids and hydroxyproline content in groundnut (Arachis hypogaea L.)

Cultivar TMV-2 of groundnut plant {Arachis hypogaea L.) was grown in a nutrient solution containing fluchloralin at the rate of either 2 mg litre^-1 or 4 mg litre“¹. Protein synthesis and hydroxyproline content in the cell walls of roots, stem and leaves were determined. Free amino acids content and total ammonia in leaves and roots were also analysed. Presence of fluchloralin did not adversely affect protein synthesis. No significant effect of herbicide was observed on hydroxyproline content of a purified cell wall fraction of groundnut roots, stem and leaves. The total amount of ammonia increased in roots and leaves of plants which received the higher concentration of fluchloralin. With the exception of aspartic acid, asparagine, glutamic acid and glutamine, free amino acids content decreased considerably with herbicide treatment. Alanine and glycine were strongly reduced. It is suggested that transamination reactions could be affected and the process of senescence may be enhanced.     

The content of free amino acids in plasma of hens of different strains

Summary Free amino acids were estimated in the plasma of Leghorn, Cornish and White Rock hens, bred under identical conditions. It was found that the plasma of Leghorn hens had a lower content of amino acids. The differences were especially pronounced for proline, glutamic acid and glycine. It was established that a lower percentage of valine, leucine and isoleucine was typical of Leghorn hens in comparison with Cornish hens. The obtained results indicate that the level of free amino acids in blood plasma is genetically controlled