Catabolism of nutritionally essential amino acids in developing porcine enterocytes

This study was conducted using the piglet model to test the hypothesis that mucosal cells of the neonatal small intestine can degrade nutritionally essential amino acids (EAA). Enterocytes were isolated from the jejunum of 0-, 7-, 14-, and 21-day-old pigs, and incubated for 45 min in Krebs buffer containing plasma concentrations of amino acids and one of the following L-[1-¹⁴C]- or L-[U-¹⁴C]-amino acids plus unlabeled tracees at 0.5, 2, or 5 mM: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. In these cells, branched-chain amino acids (BCAA) were extensively transaminated and 15–50% of decarboxylated branched-chain α-ketoacids (BCKA) were oxidized to CO₂ depending on the age of piglets. BCAA transamination increased but their decarboxylation decreased between 0 and 14 days of age. Addition of 1 and 2 mM α-ketoglutarate to incubation medium dose-dependently stimulated BCAA transamination without affecting their decarboxylation. Western blot analysis revealed that the abundance of mitochondrial BCAA aminotransferase declined but cytosolic BCAA aminotransferase increased between 0 and 14 days of age, with the cytosolic protein being the major isoform in 7- to 21-day-old pigs. BCKA dehydrogenase protein existed primarily as the phosphorylated (inactive) form in enterocytes of newborn pigs and its levels were markedly reduced in older pigs. All measured parameters of BCAA metabolism did not differ between 14- and 21-day-old pigs. In contrast to BCAA, catabolism of methionine and phenylalanine was negligible and that of other EAA was absent in enterocytes from all ages of piglets due to the lack of key enzymes. These results indicate that enterocytes are an important site for substantial degradation of BCAA but not other EAA in the neonatal gut.     

Biosynthesis of lysine and other amino acids in the developing maize endosperm

Tracer studies with aspartic acid-[4-¹⁴C], alanine-[1-¹⁴C] acetate-[2-¹⁴C] and diaminopimelic acid-[1,(7)-¹⁴C] injected into the developing endosperm of maize revealed that the biosynthesis of lysine and other amino acids occurs in this organ. The data suggest that lysine is synthesized via the diaminopimelic acid pathway.     

Changes in concentraions of free radicals and amino acids in developing maize inflorescences and fruits

The changes in the concentration of free radicals and bound amino acids in developing maize inflorescences and fruits were ascertained. The concentration rises markedly when tissues disintegrate and desiccate. A slight increase in the concentration may be ascribed to the rise of metabolic processes connected with kernel formation.     

Current topics in the biotechnological production of essential amino acids,functional amino acids,and dipeptides

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Genetic engineering to improve essential and conditionally essential amino acids in maize: transporter engineering as a reference

Transgenic Research - Ruminants and humans are unable to synthesize essential amino acids (EAAs) and conditionally essential amino acids (CEAAs) under normal conditions and need to acquire them...     

Activity and distribution of nitrogen-metabolism enzymes in the developing maize kernel

The activities of glutamine synthetase (EC 6.3.1.2), glutamate dehydrogenase (EC 1.4.1.2), aspartate aminotransferase (EC 2.6.1.1), alanine aminotransferase (EC 2.6.1.2) and soluble protein content in the developing endosperm and embryo of normal (Oh-43) and mutant (Oh-430₂) maize were investigated. Maize inbred lines were grown under field conditions and all plants were self-pollinated. Ears for experiments were harvested over the period of 15 lo 45 days after pollination. After pollination kernel capacity for soluble protein synthesis is located mainly in the endosperm. This progressively decreases and about 40 days after pollination soluble protein synthesis is taken over by the embryo. Comparative data on the activity of the investigated enzymes in the embryo and endosperm indicate that the capacity for synthesis of glutamine and glutamate predominates in the embryo tissue, whereas transamination processes at the initial stages of the embryo development are less intensive than their counterparts in the endosperm. The roles of embryo and endosperm subsequently interchange. Biosynthetic processes of soluble precursors for protein synthesis in the embryo and endosperm of the developing kernel are mutually coordinated.     

Changes in carbohydrates,amino acids and proteins in developing seed of chickpea

Developing seeds of chickpea cultivars G-130, L-550 and 850-3/27 grown under field conditions were sampled at different stages of maturity and analysed for soluble sugars, starch, soluble nitrogen, protein nitrogen and amino acids. Fr. wt of seeds of all three cultivars decreased after 28 days of flowering while the dry wt continued to increase. Rapid starch accumulation was observed between 14 and 28 days after flowering. Starch as per cent of seed dry wt started to decrease after 28 days, while starch per seed increased till maturity. The percentage of salt-soluble proteins decreased with maturation of seed. The electrophoretic pattern revealed that deposition of seed storage protein in cotyledons occurred 14 days after flowering. Most of the biochemical activity apparently occurred between 14 and 28 days after flowering.     

Amino acid metabolism in the pedicel-placenta-chalazal region of the developing maize kernel

The pedicel-placenta-chalazal (PPCh) region is a heterogeneous maternal tissue located at the base of the endosperm. Its active role in the transport and metabolism of nitrogen compounds supplied to the endosperm has been shown by incorporation of labelled compounds, as well as by analysis of appropriate enzyme activities and the free amino acid pool. Within 30 min incubation, 60–70% of the label given in [¹⁴C]aspartate or [¹⁴C]glutamate was recovered in the organic acid fraction of the PPCh. Although the dry matter and protein content of the PPCh region was practically unchanged between days 15 and 30 after pollination, glutamate transaminase, alanine transaminase, NADP-malic enzyme and NAD-malate dehydrogenase were increased substantially. The PPCh region contains glutamine at a significantly higher concentration and alanine at a lower concentration than the endosperm. In contrast to glutamate synthase, the activity of glutamine synthetase per endosperm and per mg protein is significantly higher in the PPCh region. This implies involvement of these tissues in the transport of nitrogen compounds, mainly in the form of glutamine, as well as possible compartmentation of the glutamine-glutamate cycle in the developing maize kernel.     

Nutritionally essential amino acids and metabolic signaling in aging

Aging is associated with a gradual decline in skeletal muscle mass and strength leading to increased risk for functional impairments. Although basal rates of protein synthesis and degradation are largely unaffected with age, the sensitivity of older muscle cells to the anabolic actions of essential amino acids appears to decline. The major pathway through which essential amino acids induce anabolic responses involves the mammalian target of rapamycin (mTOR) Complex 1, a signaling pathway that is especially sensitive to regulation by the branched chain amino acid leucine. Recent evidence suggests that muscle of older individuals require increasing concentrations of leucine to maintain robust anabolic responses through the mTOR pathway. While the exact mechanisms for the age-related alterations in nutritional signaling through the mTOR pathway remain elusive, there is increasing evidence that decreased sensitivity to insulin action, reductions in endothelial function, and increased oxidative stress may be underlying factors in this decrease in anabolic sensitivity. Ensuring adequate nutrition, including sources of high quality protein, and promoting regular physical activity will remain among the frontline defenses against the onset of sarcopenia in older individuals.     

Transport, metabolism, and redistribution of xylem-borne amino acids in developing pea shoots

Amino acid metabolism and transport was investigated in the leaves of 3-week-old nonnodulated seedlings of Pisum sativum L. Xylem sap entering the shoot contained nitrate (about 5 millimolar), and amino compounds (11 millimolar) of which 70% was asparagine plus glutamine; aspartate and homoserine were also present. Mature leaves showed stable nitrogen levels and incoming nitrogen was redistributed to growing leaves. Younger leaves, still enclosed in the stipules, showed negligible rates of transpiration, suggesting that most of their nitrogen must arrive in the phloem.     

Genetic analysis of opaque2 modifier gene activity in maize endosperm

Modifier genes have been described that convert the soft endosperm of opaque2 mutants to a hard, vitreous phenotype. The mode of action and the components of the genetic system involved in this seed modification are poorly understood. We used genetic and biochemical analyses to investigate the number of opaque2 modifier genes, their mode of action and their relationship to the biochemical alterations in the modified endosperm. Using two inbred opaque2 lines, we showed that the activity of opaque2 modifier genes is influenced by the genetic background. Analysis of segregating progenies and recombinant inbred lines derived from crosses between opaque2 and modified opaque2 genotypes indicated two independent loci affecting seed opacity and density. Consistent association between endosperm modification and enhanced accumulation of the gamma-zein storage protein suggested that either this protein is directly involved in the process of seed modification, or else that a modifier gene could be tightly linked to the genes responsible for gamma-zein synthesis.     

Dielectric properties,free radicals,amino acids,and some elements in maize tissues

Data on (1) permitivity and dielectric losses, (2) free radical concentrations, and (3) potassium, sodium, magnesium, calcium, nitrogen, and amino acid contents in tissues of nodal roots, internodes, and leaves of maize plant are presented in the paper. The participation of these factors in the transport phenomenon and the degree of their cooperation in the transport process are discussed.     

Genetic analysis of opaque2 modifier loci in quality protein maize

Quality protein maize (QPM) was created by selecting genetic modifiers that convert the starchy endosperm of an opaque2 (o2) mutant to a hard, vitreous phenotype. Genetic analysis has shown that there are multiple, unlinked o2 modifiers (Opm), but their identity and mode of action are unknown. Using two independently developed QPM lines, we mapped several major Opm QTLs to chromosomes 1, 7 and 9. A microarray hybridization performed with RNA obtained from true breeding o2 progeny with vitreous and opaque kernel phenotypes identified a small group of differentially expressed genes, some of which map at or near the Opm QTLs. Several of the genes are associated with ethylene and ABA signaling and suggest a potential linkage of o2 endosperm modification with programmed cell death.