PubMed · 5035223
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H D Spitz, G Henyon, J N Sivertson. 1972-05-31. A computer program for amino acid analysis.. https://doi.org/10.1016/s0021-9673(00)88768-3
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Amino acid (AA) profiles from body fluids such as blood and urine are clinical indicators for diagnosing metabolic and hepatic diseases. Current quantitative methods, such as liquid chromatography-mass spectrometry (LC-MS) with isotopically labelled internal standards (ISs), are costly and technically demanding. This study proposes a cost-efficient alternative using structural isomers as ISs in a direct liquid infusion (DLI) tandem mass spectrometry (MS/MS) approach. The method leverages chimeric spectra and fragment intensity ratios to quantify AAs, demonstrating high linearity and precision even with a 3D ion trap mass analyser. This approach offers a viable strategy for AA quantification in preventive medicine, particularly for screening metabolic diseases such as phenylketonuria, diabetes, and liver dysfunction.
S-Adenosylmethionine serves as the methyl donor for many biological methylation reactions and provides the propylamine group for the synthesis of polyamines. S-Adenosylmethionine is synthesized from methionine and ATP by the enzyme methionine adenosyltransferase. The cellular factors regulating S-adenosylmethionine synthesis have not been well defined. Here we show that in rat hepatocytes S-nitrosoglutathione monoethyl ester, a cell-permeable nitric oxide donor, markedly reduces cellular S-adenosylmethionine content via inactivation of methionine adenosyltransferase by S-nitrosylation. Removal of the nitric oxide donor from the incubation medium leads to the denitrosylation and reactivation of methionine adenosyltransferase and to the rapid recovery of cellular S-adenosylmethionine levels. Nitric oxide inactivates methionine adenosyltransferase via S-nitrosylation of cysteine 121. Replacement of the acidic (aspartate 355) or basic (arginine 357 and arginine 363) amino acids located in the vicinity of cysteine 121 by serine leads to a marked reduction in the ability of nitric oxide to S-nitrosylate and inactivate hepatic methionine adenosyltransferase. These results indicate that protein S-nitrosylation is regulated by the basic and acidic amino acids surrounding the target cysteine.
An unusual cadmium-binding protein was purified for the first time from the blood plasma of the blue mussel, Mytilus edulis. The protein was isolated and purified to homogeneity using ammonium sulfate precipitation and immobilized metal-ion affinity chromatography. It was identified as a glycoprotein with an apparent Mr of 63 kDa and a pI of 4.8. Electrophoresis of the protein under denaturing conditions on polyacrylamide gels produced four bands of 35, 37, 39 and 29 kDa. Isoelectric focusing under denaturing conditions produced 12 closely spaced bands with pIs of 4.2 to 5.8, revealing charge microheterogeneity. Molecular proterties (Mr and pI), carbohydrate content (11.6%) and composition, high histidine content (13.7%), as well cadmium-binding property of the protein (approximate log K >/= 5.4) indicated that it is similar to the mammalian histidine-rich glycoprotein, hitherto unreported in aquatic invertebrates. The cadmium-binding ability of the protein was retained even after heat denaturation and polyacrylamide gel electrophoresis.