Methionine uptake

Chappell, L. H. (1974) Methionine uptake by larval and adult Schistosoma mansoni. Int. J. Parasitol. 4 361-369. 

The majority of PET studies in oncology have been performed with C-labeled methionine, which is relatively easy to synthesize (41-43). Because of its low uptake in the brain, ["Cjmethionine has been proven to be a sensitive and specific tool for brain tumors, able to differentiate nonneoplastic from malignant lesions (42,44). Methionine uptake reflects the amino acid transport, whereas ["Cjtyrosine has been used to quantify protein synthesis rate in brain tumors (45,46). An I-iodinated tyrosine analog (IMT) also has been proposed to assess tumor cells proliferation by means of SPECT imaging. IMT uptake in glioma cells in vitro (47) and in soft-tissue sarcomas in vivo (48) was shown to be induced by rapid proliferation. 

Langen KJ, Clauss RP, Holschbach M, Muhlensiepen H, Kiwit JC, Zilles K, Coenen HH, Muller-Gartner HW. Comparison of iodotyrosines and methionine uptake in a rat glioma model. J Nucl Med 1998 39 1596-1599. 

Weber W, Wester H, Grosu A, Herz M, Dzewas B, Feldmann H, MoUs M, Stoecklin G, Schwaiger M. 0-(2-[18F]fluoroethyl)-L-tyrosine and L-[methyl-11C] methionine uptake in brain tumors initial results of a comparative PET study. Eur J Nucl Med 2000 27 542-549. 

In the case of hyperphenylalaninaemia, which occurs ia phenylketonuria because of a congenital absence of phenylalanine hydroxylase, the observed phenylalanine inhibition of proteia synthesis may result from competition between T.-phenylalanine and L-methionine for methionyl-/RNA. Patients sufferiag from maple symp urine disease, an inborn lack of branched chain oxo acid decarboxylase, are mentally retarded unless the condition is treated early enough. It is possible that the high level of branched-chain amino acids inhibits uptake of L-tryptophan and L-tyrosiae iato the brain. Brain iajury of mice within ten days after thek bkth was reported as a result of hypodermic kijections of monosodium glutamate (MSG) (0.5—4 g/kg). However, the FDA concluded that MSG is a safe kigredient, because mice are bom with underdeveloped brains regardless of MSG kijections (106). 

Using the PETIS, real-time [ CJmethionine translocation was studied for barley. For the mechanism of Fe uptake in an Fe-delicient barley, it was found that leaf methionine does not participate in the reaction of mugineic acid synthesis, but the methionine produced in barley roots is used in the biosynthesis of mugineic acid phytosiderophores [131,132]. 

Carnitine, L-3-hydroxy-4-(trimethylammonium)butyrate, is a water-soluble, tri-methylammonium derivative of y-amino-jS-hydroxybutyric acid, which is formed from trimethyllysine via y-butyrobetaine [40]. About 75% of carnitine is obtained from dietary intake of meat, fish, and dairy products containing proteins with trimethyllysine residues. Under normal conditions, endogenous synthesis from lysine and methionine plays a minor role, but can be stimulated by a diet low in carnitine. Carnitine is not further metabolized and is excreted in urine and bile as free carnitine or as conjugated carnitine esters [1, 41, 42]. Adequate intracellular levels of carnitine are therefore maintained by mechanisms that modulate dietary intake, endogenous synthesis, reabsorption, and cellular uptake. 

Among the more interesting applications of polymer Rose Bengal is that of a sensitizer in studying the oxidation of other polymeric substrates [301]. Rose Bengal immobilized on Sepharose has been reported as a sensitizer for protein photooxidation [302], The oxygen uptake by the amino acids cysteine, hisitidine, methionine, tryptophan, and tyrosine was reported to be about 20% as much from the immobilized dye as from the free dye in aqueous solution. 

Experiments with 14C-labelled fructosyllysine (FL) in rats showed that this Amadori compound is not actively transported out of the intestines. Flowever, experiments with ligated gut segments indicated that uptake by passive diffusion is feasible, at least for e-FL, whereas a-FL and fructosylmethionine are poorly absorbed.342 The presence of FL affects the active transport of other compounds thus the active transport of threonine, proline, and glycine was lowered, but that of lysine, methionine, and galactose remained unaffected.343... 

Fig. 2.4. Uptake of methionine by Hymenolepis diminuta in Na + or Na+-free fluids of varying pH. (After Lussier et at, 1979.)...

Fig. 3 Metabolic flux distribution of C. glutamicum reflecting maximal theoretical carbon yield of lysine (a) and methionine (b) from glucose. All fluxes are given as relative molar fluxes to the glucose uptake, whereby the relative flux of a reaction is reflected by the thickness of the corresponding arrow. The data are taken from recent simulation studies [5, 76]... 

T Growth factor in insects, and reported to increase protein uptake in rats, later identified as a mixture of folic acid, vitamin B12, and nucleotides U Methylsulfonium salts of methionine... 

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