THE METABOLISM OF METHIONINE DERIVATIVES CONTAINING ³⁵S IN THE RAT BRAIN IN VIVO

Abstract

METHIONINE metabolism in oil;o, and its uptake into different organs, has received attention by a number of authors (GAITONDE and RICHTER, 1955, 1956) and the rnetabolic activity of this substance has been demonstrated (NIKLAS et a/., CLOUET and RICHTER, 1959). No attention has been paid, however, to methionine sulphoxide and methionine sulphone, the first and the second oxidation stages of methionine. The destribution of r5S]methionine sulphoxirnine in the rat has been investigated by ROTH et al. (1952) who in a later paper ( ROTH et al., 1953) suggested that the cause of the toxic effect of methionine sulphoxirnine could be the incorporation of this substance in place of methionine into the proteins. In connexion with our studies of the effect of methionine and methionine sulphoximine on epileptic fits in experimental animals ( KOLOUSEK, 1956,1958; KOLOUSEK and LODIN, 1959) we set ourselves the task of ascertaining whether or not methionine sulphoximine, and the sulphoxide and sulphone are incorporated into.proteins. M E T H O DAdult male white rats of 25C280 g were used. The [55S]-~~-methionine used was of Soviet origin and its specific activity was 800 mc/g. [35S]-~~-Methionine sulphoxide and its normer and [%]-DLmethionine sulphoximine and its normer were, in essence, prepared according to BENTLEY, MCDER- MOTT and WHITEHEAD (1951).[S5S]-~~-Methionine sulphone and its normer were prepared from [S5S]-~~-methionine by oxidation with performic acid and purification of the products by cation exchange.Methionine sulphoxide, methionine sulphone and methionine sulphoximine were injected intraperitoneally (400 mg/kg body weight), the substances containing "S being mixed with their normers so that the activity of the injected substances was about 1 mc/kg body weight. The dose of 400 mg/kg body weight was chosen because it corresponds to the paroxysmal dose of methionine sulphoximine which provokes in the rat a series of epileptic fits, the so-called sfatus epilepficus, 5-6 hr after i.p. application. Although the incorporation of [s5S]-methionine into brain has been studied before by other authors, we also applied [35S]-~~-methionine to the experimental rats (I mc/kg body weight, i.p.) for comparison with the above mentioned substances. All the applied preparations were chromatographically pure. The relatively low specific activity of the applied substances and the 24 hr duration of the experiment exclude any possibility of artefacts due to radioactive disintegration.After treatment, the experimental animals were kept in metabolic cages, according to COMMAR. receiving water ad libitum and the urine was collected in calibrated test-tubes. After 2. 6 and 24 hr the animals were killed by decapitation, the heads falling into liquid nitrogen. For each time-interval and for each substance 12 rats were used. The results are given as mean values. The frozen brain was taken from each head and ground to powder under liquid nitrogen. Samples of approximately I g in weight were further homogenized in glass homogenization test...

Phosphorylation of methionine sulfoximine by glutamine synthetase.

“…Methionine sulfoximine has long been known as a convulsion-producing agent,8' 9 and it has been known for some time that methionine sulfoximine as well as methionine sulfone and methionine sulfoxide can act as glutamic acid antagonists and as relatively effective inhibitors of glutamine synthetase.10-13 The possibility that there is a relationship between the striking inhibition of cerebral glutamine synthetase by methionine sulfoximine and the dramatic effect of this amino acid on the central nervous system has inspired a number of interesting speculations and experiments.9' [14][15][16][17][18][19][20][21][22] Indeed, it seems highly probable that glutamine synthetase performs a signlificant function in the central nervous system and therefore that inhibition of this enzyme would be associated with substantial physiological effects.…”