The distribution of amino acids in the genetic code

By introducing a mutational deterioration functionMD and a principle of approximate minimum of the function, we have deduced the distribution of amino acids in genetic code, which includes the degenracy rule of codons, the global extreme of genetic code from codon interactions and the hydrophobicity domain of the prevalent (standard) code.The project supported by National Science Foundation of China.     

Formation of specific amino acid sequences during thermal polymerization of amino acids

The mechanism of the thermal polymerization (at 180°C) of glutamic acid, tyrosine, and glycine has been studied. Glutamic acid is quickly and almost completely converted into pyroglutamic acid. The only dipeptide that is formed by dimerization of the remaining two amino acids is cyclic glycyl-tyrosine (a diketopiperazin). In a secondary reaction pyroglutamic acid interacts with cyclic glycyl-tyrosine and yields pyroglutamyl-glycyltyrosine and pyroglutamyl-tyrosyl-glycine. Other di- or tripeptides are not observed. The preferential appearance of the two pyroglutamyl-peptides has been reported earlier by Nakashima et al. (1977). The present data explain those results. Model experiments show that cyclic glycyl-tyrosine can also be cleaved by other acids or bases. In the presence of acetic acid at 118°C N-acetyl-glycyl-tyrosine is the major product. Partial hydrolysis predominantly yields tyrosyl-glycine. These effects are explained by stereospecific interactions. The results on self-ordering of amino acids during peptide formation are discussed in respect of the origin of prebiotic enzymes and genetic information.     

Compartmental analysis of plasma and liver n-3 essential fatty acids in alcohol-dependent men during withdrawal

The mechanism by which chronic ethanol consumption reduces concentrations of long chain polyunsaturated (LCP) fatty acids (FA) in tissues of humans was investigated in alcohol-dependent (AD) men during early withdrawal and to a well-matched control group by fitting the concentration-time curves of d(5)-labeled n-3 FA from plasma and liver, which originated from an oral dose of d(5)-linolenic acid (d(5)-18:3n-3) ethyl ester to a compartmental model. Blood sampled over 168 h and a liver specimen obtained 96 h after isotope administration were analyzed for d(5)-18:3n-3, d(5)-20:5n-3, d(5)-22:5n-3, and d(5)-22:6n-3. Plasma 20:5n-3 and 22:5n-3 were lower in AD subjects, compared with controls (20:5n-3: -50%, 22:5n-3: -34%). Increased amounts of d(5)-18:3n-3 were directed toward synthesis of d(5)-20:5n-3 in AD subjects (P < .05). However, this effect was offset by larger amounts of 20:5n-3 lost from plasma (control: 2.0 vs. AD: 4.2 mg d(-1)). In livers of AD subjects, more d(5)-18:3n-3 and d(5)-22:5n-3 were utilized for synthesis of d(5)-20:5n-3 (+200%) and d(5)-22:6n-3 (+210%), respectively, than was predicted from plasma kinetics. Although, the potential to utilize linolenic acid for synthesis of LCP FA was greater in AD subjects compared with controls, heightened disappearance rates of 20:5n-3 reduced overall plasma concentrations of several endogenous n-3 LCP FA.     

The release of amino acids from nerve during stimulation

Frog sciatic nerves were incubated for 24 hours in either glycine, aspartic acid, glutamic acid, lysine, leucine, γ-aminobutyric acid, glutamine, or pentanedioic acid (all labeled with C¹⁴), and the rates of release of these compounds were monitored under resting conditions and during stimulation. Upon stimulation, the rate or release of glutamic acid increased an average of 200% above the resting rate. This extra release is highly specific with regard to molecular size and structure, since of the compounds tested only glutamic acid gave significant increases in rates of release during stimulation. Ouabain (0.1 mM) had no effect on the rate of release; however, sodium azide (0.2 mM or 1.0 mM) completely eliminated the extra release during excitation, indicating that the increased permeability to glutamic acid is energy-dependent. Competition experiments show that the extra release of glutamic acid can be eliminated with 10 mM concentrations of non-isotopic choline. The hypothesis is advanced that glutamic acid is actively extruded by a highly specific carrier mechanism.     

太湖水体溶解性氨基酸的空间分布特征

为探索氨基酸(DAAs)组分特征对生物可利用性溶解有机质(DOM)的示踪及定量表征可能性, 对太湖3个湖区(北太湖: 藻型湖区,东太湖: 草型湖区, 南太湖: 农业污染湖区)水体DAAs浓度、组分特征及其空间变化进行了调查研究,并对控制其量、质空间分布的因素加以讨论。结果表明夏季太湖水体DAAs的浓度范围为0.27-3.95 μmol/L,平均值为(1.38±1.17)μmol/L,与湖泊、海洋中研究中报道结果相近。北太湖、南太湖、东太湖3个湖区的DAAs浓度平均值分别为(2.59±0.71)μmol/L,(0.48±0.14)μmol/L,(0.48±0.16)μmol/L,北太湖DAAs浓度及对有机碳氮的贡献都明显高于其他湖区,DAAs组分中以苯丙氨酸和赖氨酸为主,而在南太湖和东太湖,赖氨酸都是最主要的DAAs组分。表明水体的DAAs组分特征能对湖泊营养状态及生态类型的变化做出响应,可以作为指示湖泊营养状态的生物标记物。DAAs也可以作为DOM 生物降解性的评价参数,反映湖泊水体中与生物活性相关的DOM 动态变化。根据氨基酸对有机碳的贡献估算出北太湖的活性溶解性有机碳相对含量为(17.65±17.84)%,显著高于南太湖和东太湖。但由于太湖高度的空间异质性,还需要在今后的研究工作中进行相关的室内实验,建立适用于太湖的经验公式。     

Compartmental distribution of beta-hexosaminidase isoenzymes in I-cell fibroblasts.

A characteristic of the human lysosomal disorder I-cell disease is an abnormal excretion of most lysosomal hydrolases, including beta-N-acetyl-D-glucosaminidase (EC 3.2.1.30; beta-hexosaminidase) by cultured skin fibroblasts. Treatment of I-cell cultures with cycloheximide or tunicamycin demonstrated that (1) I-cell fibroblasts rapidly excrete all newly synthesized beta-hexosaminidase, (2) two qualitatively distinct pools of beta-hexosaminidase isoenzymes exist inside I-cell fibroblasts, one of which is a rapid-turnover excretory pool, and (3) the induction of an abnormal glycosylation of beta-hexosaminidase by tunicamycin in normal or I-cell fibroblast cultures does not affect subsequent excretion of the enzyme.     

Compartmental modeling of postprandial dietary nitrogen distribution in humans

A linear 11-compartment model was developed to describe and simulate the postprandial distribution of dietary nitrogen. The values of its 15 constant diffusion coefficients were estimated from the experimental measurement of (15)N nitrogen kinetics in the intestine, blood, and urine after the oral administration of (15)N-labeled milk protein in humans. Model structure development, parameter estimation, and sensibility analysis were achieved using SAAM II and SIMUSOLV softwares. The model was validated at each stage of its development by testing successively its a priori and a posteriori identifiability. The model predicted that, 8 h after a meal, the dietary nitrogen retained in the body comprised 28% free amino acids and 72% protein, approximately 30% being recovered in the splanchnic bed vs. 70% in the peripheral area. Twelve hours after the meal, these values had decreased to 18 and 23% for the free amino acid fraction and splanchnic nitrogen, respectively. Such a model constitutes a useful, explanatory tool to describe the processes involved in the metabolic utilization of dietary proteins.     

Administration of branched-chain amino acids during sustained exercise--effects on performance and on plasma concentration of some amino acids.

Previous studies have shown that sustained exercise in human subjects causes an increase in the plasma concentration ratio of free tryptophan: other large neutral amino acids [including the branched-chain amino acids (BCAA)]. This should favour the transport of tryptophan into the brain and also the synthesis of 5-hydroxytryptamine, which is thought to contribute to fatigue during prolonged exercise. A mixture of the three BCAA was given to subjects during a 30-km cross-country race or a marathon (42.2 km) and the effects on mental and physical performances were measured. The mental performance, measured as the performance in the Stroop Colour and Word Test (CWT), was improved after, as compared to before the 30-km cross-country race when a BCAA supplement was given during the race, whereas the CWT scores were similar before and after in the placebo group. The running performance in the marathon was improved for the "slower" runners (3.05 h-3.30 h) when BCAA was taken during the race; however, there was no significant effect on the performance in the "faster" runners (less than 3.05 h). The results showed that both mental and physical performance was improved by an intake of BCAA during exercise. In addition, the effects of exercise on the plasma concentration of the aromatic amino acids were altered when a BCAA supplement was given during the marathon.