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81.
Summary Aside from its role as one of the limiting essential amino acids in protein metabolism, tryptophan (TRP) serves as precursor for the synthesis of the neurotransmitters serotonin and tryptamine as well as for the synthesis of the antipellagra vitamin nicotinic acid and the epiphyseal hormone melatonin.By involvement in so manifold pathways, TRP and its metabolites regulate neurobehavioral effects such as appetite, sleeping-waking-rhythm and pain perception. TRP is the only amino acid which binds to serum albumin to a high degree. Its transport through cell membranes is competetrvely inhibited by large neutral amino acids (NAA). The TRP/NAA ratio in plasma is essential for the TRP availability and thus for the serotonin synthesis in the brain.Due to its high TRP-concentration, human milk protein provides optimal conditions for the availability of the neurotransmitter serotonin. Low protein cow's milk-based infant formulas supplemented with-lactalbumin — a whey protein fraction containing 5.8% TRP — present themselves as a new generation of formulas, with an amino acid pattern different from the currently used protein mixtures of adapted formulas, resembling that of human milk to a much higher degree. 相似文献
82.
一种用聚乙二醇制备微粒体的方法 总被引:8,自引:0,他引:8
介绍一种用聚乙二醇(PEG)制备微粒体的方法.大鼠肝匀浆经聚乙二醇-6000凝聚,及两次高速离心即可得到微粒体组分,与超速离心方法比较,可省去超速离心步骤,又缩短了分离制备的时间,是一种比较简单易行的方法. 相似文献
83.
While the dietary importance of proteins, essential fatty acids, vitamins and trace elements has been well recognised, the
role of shadow nutrients, a class of metabolites, which are biosynthesized in the body and serve vital functions, such as
lipoic acid, choline, inositol, taurine and carnitine, has not been adequately appreciated. There are reasons to believe that
during infancy and in ageing, biosynthesis of these metabolites may be limited. The objective of this review is to highlight
the essentiality of these nutrients and the need for their supplementation in the diets of infants and in elderly people.
Provision of shadow nutrients where the necessary biosynthetic machinery might not have developed to full stature or might
have slowed down, is a new concept in nutrition which needs attention. 相似文献
84.
Daan Kuiper 《Physiologia plantarum》1982,56(4):436-443
The Mg2+ - and Ca2+ -stimulated ATPase activities of the microsomal fractions of the roots of four inbred lines of Plantago major L. were followed at two levels of mineral nutrition. In addition the response of a transfer of plants from one condition to the other was studied. Kinetic properties of the ATPases (Km and Vmax ) were calculated and used to differentiate between genetic differences among the inbred lines and the plasticity within each inbred line. The Vmax values of the ATPase activity differed significantly between the lines and were directly related to seed number per capsule (low Vmax → 11 seeds per capsule, high Vmax → 33 seeds per capsule). In addition, the Vmax values of the ATPase acitivty may be related to ecological strategy. Plasticity of enzyme activity is expressed in differences in the Vmax values of the ATPase activity, as a response to nutritional level or changes of the strength of the nutrient solution. Differences in this plasticity in the four selected lines and in rapidity of response to a change in mineral nutrition were directly related to the ecological strategy. These results are discussed in relation to the strategy of the genotypes for survival in the field. The presence of plasticity in line 4 (ssp. pleiospema ) makes this genotype behave like an annual plant, following a ruderal strategy. The absence of plasticity in line 1 (ssp. major ) fits a more competitive strategy. 相似文献
85.
A green house study was conducted on the effect of P and Zn on nodulation and N fixation in chickpea (Cicer arietinum L.) in a loamy sand (Typic Torripsamments) using treatment combinations of five levels of P (0, 25, 50, 100 and 250 ppm),
and six levels of Zn (0, 5, 10, 20, 40 and 100 ppm). The number, dry matter and leghaemoglobin content of nodules, and amount
of N fixed generally increased with Zn alone upto 19 ppm and P alone upto 50 ppm, and decreased with their higher levels.
Application of 25 to 50 ppm P and 5 to 10 ppm Zn counteracted to a greater extent the adverse effect of 40 and 100 ppm Zn,
and 250 ppm P, resp. Maximum nodulation and N fixation (91 to 145% over zero P and Zn, at maturity) was recorded with 25 to
50 ppm P applied along with 5 to 10 ppm Zn. At 64 days, depletion in soil-N was noted, particularly when P was applied, whereas
at maturity there was a gain in soil-N, ranging from 10.5 to 44.5 kg/2×106 kg soil depending upon P and Zn treatments. The increase in nodulation and N fixation with balanced P and Zn nutrition might
be attributed to an increase in leghaemoglobin, and K and Fe concentration in nodules, and increased plant growth, resulting
into enhanced activity of N fixing organisms. The results showed that balanced P and Zn nutrition is essential not only for
plant growth but also for maximum activity of Rhizobium for N fixation.
Work done at Harvana Agricultural University, Hissar, India. 相似文献
86.
Activity of ribulose 1,5-bisphosphate (RuBP) carboxylase in leaf extracts of the constitutive Crassulacean acid metabolism (CAM) plant Kalanchoe pinnata (Lam.) Pers. decreased with increasing leaf age, whereas the activity of phosphoenolpyruvate (PEP) carboxylase increased. Changes in enzyme activities were associated with changes in the amount of enzyme proteins as determined by immunochemical analysis, sucrose density gradient centrifugation, and SDS gel electrophoresis of leaf extracts. Young developing leaves of plants which received high amounts of NO
3
-
during growth contained about 30% of the total soluble protein in the form of RuBP carboxylase; this value declined to about 17% in mature leaves. The level of PEP carboxylase in young leaves of plants at high NO
3
-
was an estimated 1% of the total soluble protein and increased to approximately 10% in mature leaves, which showed maximum capacity for dark CO2 fixation. The growth of plants at low levels of NO
3
-
decreased the content of soluble protein per unit leaf area as well as the extractable activity and the percentage contribution of both RUBP carboxylase and PEP carboxylase to total soluble leaf protein. There was no definite change in the ratio of RuBP carboxylase to PEP carboxylase activity with a varying supply of NO
3
-
during growth. It has been suggested (e.g., Planta 144, 143–151, 1978) that a rhythmic pattern of synthesis and degradation of PEP carboxylase protein is involved in the regulation of -carboxylation during a day/night cycle in CAM. No such changes in the quantity of PEP carboxylase protein were observed in the leaves of Kalanchoe pinnata (Lam.) Pers. or in the leaves of the inducible CAM plant Mesembryanthemum crystallinum L.Abbreviations CAM
Crassulacean acid metabolism
- RuBP
ribulose 1,5-bisphosphate
- PEP
phosphoenolpyruvate
- G-6-P
glucose-6-phosphate 相似文献
87.
Summary Dry-matter accumulation, and concentration and uptake of nitrogen increased with increasing level of nitrogen at all the stages of crop growth. The differences in nitrogen concentration due to nitrogen levels were greatest at panicle initiation stage and started becoming narrower with the advancement in crop age. Split application of nitrogen with its heavier fractions at tillering and panicle initiation stages either through soil alone or soil+foliage (1/3+1/3+1/3) resulted in higher dry-matter accumulation, and higher nitrogen concentration and uptake than other methods. The crop, on an average, removed 61 kg N/ha. Plants accumulated nearly 15% of the total absorbed nitrogen, up to tillering, 50% up to panicle initiation and 85–90% up to heading. Proportionately lesser nitrogen uptake and dry-matter accumulation at post-heading stage is an indicative of a major constraint for production efficiency of rainfed-upland rice culture. 相似文献
88.
Summary Inclusion of sucrose in the solution applied to soybean (Glycine max L. merr.) leaves much reduced the severity of the damage to the leaves from application of urea and, to a lesser extent, from application of phosphorus (P) as orthophosphoric acid. Sucrose had no evident effect on P absorption. Damage to the leaves from joint application of orthophosphoric acid and urea exceeded the sum of the damage caused by the substances individually. Urea did not seem to influence P absorption, but the effect, if any, was not readily determined because nearly all values for P absorption exceeded 90%.Neutralization of orthophosphoric acid with nitrogen-containing organic bases, including choline, guanidine, and guanyl urea, did not prove useful as a technique for increasing the quantity of orthophosphate that could be applied without damage to the leaves.Absorption and translocation of orthophosphate by corn (Zea mays L.) and soybean leaves were not influenced by the pH of the solution within the range from 2 to 10. Absorption of tripolyphosphate by corn leaves decreased with an increase in pH of the solution applied, but translocation of the absorbed P was not influenced by pH. With soybeans, absorption of tripolyphosphate decreased with an increase in pH of the solution. Translocation of P applied to soybean leaves as tripolyphosphate was less than 5% of the amount absorbed within the first 24 hr and decreased with an increase in pH after 10 days. 相似文献
89.
Meredith F. Small 《International journal of primatology》1981,2(1):91-95
Using weight and skinfold thickness to calculate relative body fat, the fat content of 21 captive female rhesus macaques was
estimated. Although age and. pregnancy had no effect on fat, rank was significant, especially during winter, with high-rank
females having the highest fat scores. Rank therefore has a significant effect on the health of captive animals and may also
affect the health of individuals in feral groups. 相似文献
90.
褐藻寡糖(alginate oligosaccharides,AOS)是褐藻胶的降解产物,具有抗氧化、调节免疫、调节血脂、促进细胞生长等生理活性,应用范围广泛。现有的AOS 制备法主要分为物理法、化学法和生物法。介绍AOS的生物法制备包括酶解、微生物全细胞发酵和生物合成法,基因工程的应用在改造产褐藻胶裂解酶的菌株以提高生物法效率方面具有重要意义。此外,规模化的AOS生物法制备案例进行了科学引证,并展望了未来 AOS规模化制备的发展方向,以期为 AOS 的工业化制备和应用提供参考。 相似文献