Organ and Intracellular Location of the Methionine Methyl Group Synthesizing System of the Rat.

Abstract

Many publications have dealt with the de novo biosynthesis of the methionine methyl group by animal systems in vitro( 1-S), but no work has been reported on the organ and intracellular location of this biosynthetic system. This is the purpose of this communication.Procedures. To determine which organs were the most active in synthesizing methionine methyl groups, 2 rats were used in each of 3 experiments. The brain, pectoralis * This work was supported in part by a PHS grant 2.G-627 to P. Gyorgy, M. D. muscles, kidneys, and liver were removed immediately upon killing. The tissues were rinsed, patted dry, weighed, and homogenized in a Servall "Omni-mixer" at full speed at 0°C for 2 minutes with 4 ml of 0.05 M phosphate buffer (pH 7.2) per g of tissue. The homogenates were then centrifuged at ca. 25,000 X g for 3 hours at 0°C and the supernatants used in the assays.In the investigations on the intracellular location, the liver was used because of results obtained in the first part of this study, a single rat being used per experiment. After

Brain tumor protein synthesis and histological grades: A study by positron emission tomography (PET) with C11-L-Methionine

“…L. MET was proved to be one of the best substrates for the study of brain neutral amino-acid transport system (type L) at the blood-brain barrier (BBB) and neuronal membrane level (7, 8). As an essential amino-acid (9), L. MET is not synthetized or recycled in brain ceils (10,11) and its intracellular incorporation is dependant on the external supply provided by blood to the brain through the BBB (12,13,14,15,16). Transmethylation pathways, physiologically very important, involve in brain less than 1% to 2% per hour of the mass of MET taken by glial and neuronal cells (17,18,19,20).…”

Methionine Recycling in Brain: A Role for Folates and Vitamin B‐12

“…Wnlike liver and kidney, which contain two enzymes that can synthesize methionine from homocysteine (betaine-homocysteine methyl-' transferase (EC 2.1.1.5) and the folate-dependent methyltransferase (EC 2.1.1.13), brain contains only the latter, B-12 -dependent enzyme (Finkelstein et al, 1971). Direct experiments with tissue homogenates were unable to detect any methylation of homocysteine to methionine in brain, unlike liver, kidney, and muscle (Langer, 1964). Since there is carrier-mediated transport of methionine from blood into brain, it is possible that the entire brain requirement for methionine comes from blood (Rapoport, 1976).…”

An In Vivo Kinetic Model with L‐[35S]Methionine for the Determination of Local Cerebral Rates for Methionine Incorporation into Protein in the Rat

“…Therefore, kinetic studies with ~-[~'SlMet estimate the sum of the two reaction pathways (protein synthesis and transmethylation pathway). In fact, Met has a small metabolism toward the transmethylation pathway (Langer, 1964;Spector et al, 1980), all the more so as the course of the kinetic study is limited to 90 min. Moreover, the tissue radioactivity due to [35S]adenosylmethionine and [35S]aden~~ylhom~cy~teine in whole brain using HPLC according to Gharib et al (1982) was measured 90 min after an intravenous injection of L- [?5]Met in five normal rats.…”