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PubMed1985

The effect of perinatal anoxia on amino acid metabolism in the developing brain. Part II: The effect of perinatal anoxia on the free amino acid patterns in CSF of infants and children.

To clarify the effects of perinatal anoxia on the subsequent amino acid metabolism in the brain of children, free amino acid levels in the cerebrospinal fluid (CSF) were determined in 15 children diagnosed as having cerebral palsy and/or mental retardation with perinatal anoxia, and 58 control children without anoxia, aged from 4 days to 12 yrs. There was no significant difference in total amino acid levels between anoxic children and the controls. In the controls, the Gln level in CSF was high, Arg, Asp and Glu levels in CSF were almost the same during infancy and childhood, and the levels of Orn, Lys, His, Tau, Thr, Ser, Asn, Gly, Ala, Val, Met, Ile, Leu, Tyr and Phe in CSF decreased with age until pre-school age. In the newborns and infants among the anoxic children, the levels of most free amino acids in CSF were relatively high compared with those of the controls and, except Glu and Gln, decreased with age during infancy. The Orn, His, Gly, Tyr and Phe levels in CSF of anoxic children were lower than those of the controls in older infants. These results suggest that perinatal anoxia affected free amino acid patterns in CSF of newborns and infants and that the subsequent disturbance of amino acid metabolism in their brains remained after birth.

Amino Acids↗
PubMed1987

1987 McCollum award lecture. Kinetics of human amino acid metabolism: nutritional implications and some lessons.

Clinical nutrition is an integrative science with the ultimate purpose of defining in quantitative terms the characteristics of an optimum nutritional intake in relation to a defined level of nutritional health. Thus, to achieve major progress in our field of clinical nutrition, data from the molecular, subcellular, cellular, and organ levels need to be exploited and considered in reference to the whole organism; this requires that we identify important unanswered questions for this latter and more complex, hierarchical level of biological organization and then pursue the answers with the aid of techniques and approaches used in and concepts emerging from all areas of modern biology. In relation to this, the present overview of some of the studies that my colleagues, my students, and I have conducted was meant to emphasize that there is considerable merit in attempting to explore the integrative aspects of the physiology and biochemistry of human nutrient metabolism, specifically of amino acids, with the aid of stable-isotope probes. Recognition of the importance of the phosphorylation and dephosphorylation of cellular proteins as a major regulatory process and of the regulation of leucine oxidation through changes in the activity of the branched-chain 2-Oxo acid dehydrogenase complex via a reversible phosphorylation catalyzed by a specific branched-chain dehydrogenase kinase and phosphatase is indeed exciting new knowledge. Following from this, Espinal et al state: "The activity of the complex determines the rate of degradation and the dietary requirement for branched-chain amino acids." However, the physiological situation cannot be appreciated simply in these terms because we showed that the rate of oxidation of leucine depends upon the tissue availability of the amino acid. Furthermore, our studies revealed that the regulation of leucine oxidation in the intact human appears to be achieved through biochemical mechanisms that are linked to the host's nutritional requirements. These observations and interpretations would not have emerged by considering only the enzymology of branched-chain amino acid metabolism; this underscores the value of exploring, through use of safe noninvasive tracer techniques, the communication of amino acid metabolism among different systems and how these systems might interplay to influence the nutritional needs of the individual. This recalls Fishman's advice: "Physiology has a special role to play here, for after probing the submicroscopic, life is left behind. It is physiology's responsibility to put together the lifeless pieces of the molecular biologist into living systems."(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗
PubMed1986

Amino acid metabolism in pituitary adenomas.

Patients with pituitary adenomas were examined with positron emission tomography with the administration of 11C-labelled methionine. In a few patients comparative studies using the two stereo-isomers L- and D-methionine were also performed. The results showed a rapid distribution of D-methionine within the tumor tissue without signs of irreversible trapping of the tracer. L-methionine on the other hand was rapidly irreversibly trapped indicating the metabolic fate. It is concluded that 11C-L-methionine can be used to quantify amino acid metabolism in the tumors. The amino acid metabolism was evaluated in a group of adenomas before and after treatment with bromocriptine. The results indicate a marked reduction of the amino acid metabolism in prolactinomas amounting to 60%. These tumors at a later time responded with tumor shrinkage. Hormonally inactive tumors showed no effect of treatment.

Adenoma↗
PubMed1979

The role of blood-brain barrier transport of tryptophan and other neutral amino acids in the regulation of substrate-limited pathways of brain amino acid metabolism.

Many pathways of essential neutral amino acid metabolism in the CNS are influenced by precursor availability. Since the delivery of circulating amino acids to brain cells is primarily controlled by the rate of amino acid transport through the blood-brain barrier (BBB), pathways of brain amino acid metaboliransport system. The Km of BBB transport is in the 0.1--0.6 mM range, which approximates the physiologic plasma levels and forms the basis of the unusual sensitivity of the brain to competition effects on neutral amino acid transport. Unlike the brain, the Km of amino acid transport into other organs is in the 1--10 mM range or greater, which frees these tissues from competition effects in the physiologic range of plasma amino acids. Tryptophan circulates 80--90% bound to albumin; however, the capacity/affinity ratio of the BBB neutral amino acid transport system exceeds the capacity/affinity ratio of albumin binding of tryptophan, which enables the carrier to strip tryptophan off albumin as it traverses the brain capillary. The activity of the BBB neutral amino acid transport system is probably not modulated by insulin, but is influenced by changes in thyroid hormone status; the transport system is also induced in states of hepatic encephalopathy and this induction process is the primary cause of the increased brain tryptophan and serotonin levels in cirrhosis.

Animals↗
PubMed1992

[Prenatal diagnosis of inborn error of amino acid metabolism].

Prenatal diagnosis of inborn errors of amino acid metabolism was discussed from the viewpoints of its purpose, ethical problems, analysis methods, and sampling methods of the fetal tissues. In addition to the general discussion, our results of the prenatal diagnosis of 20 cases with nonketotic hyperglycinemia (NKH) were also reported. Nineteen cases were diagnosed by the enzymatic method, while one Finnish case was successfully diagnosed by DNA analysis, which is based on our observation that a missense mutation we identified accounts for 70% of the mutant alleles in Finland. The DNA analysis would be a great help for the prenatal diagnosis in Finland where the incidence of NKH is unusually high (1: 12,000 births).

Amino Acid Metabolism, Inborn Errors↗
PubMed1998

Amino acid metabolism and the energetics of growth.

The nonessential amino acids are involved in a large number of functions that are not directly associated with protein synthesis. Recent studies using a combination of transorgan balance and stable isotopic tracers have demonstrated that a substantial portion of the extra-splanchnic flux of glutamate, glutamine, glycine and cysteine derives from tissue synthesis. A key amino acid in this respect is glutamic acid. Little glutamic acid of dietary origin escapes metabolism in the small intestinal mucosa. Furthermore, because glutamic acid is the only amino acid that can be synthesized by mammals by reductive amination of a ketoacid, it is the ultimate nitrogen donor for the synthesis of other nonessential amino acids. Because the synthesis of glutamic acid and its product glutamine involve the expenditure of adenosine triphosphate (ATP), it seems possible that nonessential amino acid synthesis might have a significant bearing on the energetics of protein synthesis and, hence, of protein deposition. This paper discusses the topic of the energy cost of protein deposition, considers the metabolic physiology of amino acid oxidation and nonessential amino acid synthesis, and attempts to combine the information to speculate on the overall impact of amino acid metabolism on the energy exchanges of animals.

Adenosine Triphosphate↗
PubMed2002

Methods for measuring sulfur amino acid metabolism.

PURPOSE OF REVIEW: The importance of sulfur amino acid metabolism has become increasingly apparent in recent years. Methionine and cysteine are precursors of glutathione, which plays an important role in intracellular antioxidant/free radical defenses. Homocysteine is a non-protein-bound sulfur amino acid strongly implicated in the pathogenesis of several diseases. Both glutathione and homocysteine are affected by abnormalities in sulfur amino acid metabolism that occur in the clinical setting. RECENT FINDINGS: The Storch-Young model, which determines methionine turnover and homocysteine remethylation by means of a tracer methionine infusion, has been improved by using plasma homocysteine (rather than methionine) enrichment in the model. A complex new tracer method involving the use of tracer serine, methionine, and leucine has been described to determine the effects of folate or pyridoxine deficiency on sulfur amino acid-methyl transfer reactions in humans. The etiology of hyperhomocysteinemia in chronic renal failure is controversial; new concepts in this area are described. There is new interest in the subspecies of homocysteine in the circulation. A new method is described for measuring the extremely low plasma concentrations of reduced homocysteine, using gas chromatography-mass spectrometry. Plasma S-adenosylhomocysteine, measured by fluorescence high-performance liquid chromatography, has been suggested as being superior to homocysteine as a predictor of the risk of vascular disease. SUMMARY: This review highlights and critiques the above recent developments, and points out some of the complexities and pitfalls in designing and interpreting human metabolic studies involving the sulfur amino acids.

Amino Acids, Sulfur↗
PubMed1997

Short-term dynamics in protein and amino acid metabolism.

Actual amounts of free amino acids in the blood are sufficient to support whole body protein synthesis for some minutes only. This indicates that the levels of free amino acids in the circulation are kept small and constant relative to the amounts of amino acids supplied by daily intake and turnover of body proteins. The clearance of the amino acids originating from either endogenous or exogenous sources is mainly due to protein synthesis and metabolic degradation. The partitioning of dietary amino acids between these processes, on the short term, is supposed to play an important role in whole body amino acid economy. Therefore whole body amino acid economy could be improved by nutritional measures that favour the clearance of dietary amino acids by protein synthesis instead of by metabolic degradation. These nutritional measures should to be focused on threshold values for metabolic degradation of individual amino acids.

Amino Acids↗
PubMed2004

Potential of fermentation profiling via rapid measurement of amino acid metabolism by liquid chromatography-tandem mass spectrometry.

Monitoring amino acid metabolism during fermentation has significant potential from the standpoint of strain selection, optimizing growth and production in host strains, and profiling microbial metabolism and growth state. A method has been developed based on rapid quantification of underivatized amino acids using liquid chromatography-electrospray tandem mass spectrometry (LC-MS-MS) to monitor the metabolism of 20 amino acids during microbial fermentation. The use of a teicoplanin-based chiral stationary phase coupled with electrospray tandem mass spectrometry allows complete amino acid analyses in less than 4 min. Quantification is accomplished using five isotopically labeled amino acids as internal standards. Because comprehensive chromatographic separation and derivatization are not required, analysis time is significantly less than traditional reversed- or normal-phase LC-based amino acid assays. Intra-sample precisions for amino acid measurements in fermentation supernatants using this method average 4.9% (R.S.D.). Inter-day (inter-fermentation) precisions for individual amino acid measurements range from 4.2 to 129% (R.S.D.). Calibration curves are linear over the range 0-300 microg/ml, and detection limits are estimated at 50-450 ng/ml. Data visualization techniques for constructing semi-quantitative fermentation profiles of nitrogen source utilization have also been developed and implemented, and demonstrate that amino acid profiles generally correlate with observed growth profiles. Further, cellular growth events, such as lag-time and cell lysis can be detected using this methodology. Correlation coefficients for the time profiles of each amino acid measured illustrate that while several amino acids are differentially metabolized in similar fermentations, a select group of amino acids display strong correlations in these samples, indicating a sub-population of analytes that may be most useful for fermentation profiling.

Amino Acids↗