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Because the amino acids 11C L-leucine, 11C L-methionine, and 11C D-methionine are used for examinations of brain tumors with positron emission tomography (PET), the uptake of the corresponding 14C substances and their incorporation into protein was studied in the rat brain. The uptake of all three substances from the plasma, across the blood-brain barrier, and into the brain took place quite quickly; return to the plasma seemed negligible. Incorporation into protein took place much more slowly.

11C-labeled L- and D-methionine uptake was measured in seven patients with brain tumors using positron emission tomography. Tumors accumulated both isomers of the tracer. The strongest uptake occurred in tumors with a high grade of malignancy, while low grade tumors accumulated less activity. The L to D uptake ratio in tumor regions ranged from 0.92-1.25. Conventional 99mTc-DTPA scans revealed blood-brain barrier damage in two patients with no or only slight 11C-methionine accumulation, while one patient with a negative 99mTc-DTPA scan accumulated 11C-methionine in the tumor region. In view of the biochemical pathway of methionine and the present findings, it is concluded that the uptake reflects metabolic activity in brain tissue rather than uptake by diffusion due to disruption of the blood-brain barrier.

Four patients with radiologically normal pituitary gland were examined with positron emission tomography after the administration of (methyl-11C)-L-methionine. On a following day the examination was repeated with (methyl-11c)-D-methionine. The accumulation rate of L-methionine in the pituitary was measured, giving a value that was about twice that of normal brain tissue. The accumulation rate of D-methionine in the pituitary was almost a factor of 10 lower than that of L-methionine. In the normal brain tissue that ratio was 2.3. The study clearly indicates that the methionine uptake in the pituitary is stereospecific. 11C-D-methionine is freely distributed in the tissue without entrapment, whereas 11C-L-methionine is irreversibly bound. It is concluded that PET with 11C-L-methionine can be used to study amino acid utilization in the pituitary.

Two species of the fungus Cephalosporium form increased amounts of cephalosporin N (synnematin B) when grown in natural media supplemented with D-methionine. Only those derivatives of methionine that were easily converted into methionine were effective in increasing the accumulation of cephalosporin N. Neither of the two adjacent homologs of methionine increased the amount of biologically active penicillin formed. No evidence was obtained for the production of a penicillin different from cephalosporin N. d -Methionine is presumed to be effective in increasing the concentration of cephalosporin N by reason of its incorporation into the terminal portion of the d -α-aminoadipic acid side chain of the penicillin molecule.

Summary1) Ethionine inhibition of induction of enzymes involved in benzoate oxidation by washed cell suspensions of Pseudomonas aeruginosa is rapidly reversed by L-methionine and almost as rapidly by D-methionine. Neither amino acids nor ethionine have any effect once the enzymes have been induced. Similar results were obtained with p-fluorophenylalanine.

d-Methionine and d-tyrosine, crystallized from water as microcrystals, were studied by applying the techniques of X-ray powder diffractometry. d-methionine is monoclinic with a = 15.189(4), b = 10.298(3), c = 9.435(3) A, β = 92°28 (1)′, Z = 8, Dm = 1.325(5), Dx = 1.343 Mg m−3, V = 1474(1) A3, and space group P21. d-Tyrosine is orthorhombic with a = 20.716(6), b = 13.736(4), c = 5.842(2) A, Z = 8, Dm = 1.425(5), Dx = 1.447 Mg m−3, V = 1662(2) A3 and space group P2122. The JCPDS Diffraction File Nos. are: 37-1997 for d-tyrosine; 37-1998 for d-methionine.