Zur Bestimmung von kleinen Mengen Methionin im Gewebe

Abstract

Condensation products of homocysteine and cysteine with formaldehyde yield colored solutions with sodium nitroprusside in the McCarthy-Sullivan reaction. This effect interferes with the determination of methionine in tissue preparations. The condensation product from homocysteine and formaldehyde (H-F) is a fairly stable, heterocyclic 6-membered ring. The optimum yield of H-F is obtained after 30 minutes at pH 5 and 40[degree]C. The compound is resistant to boiling in acid solution. An analogous product is formed from homocystine and formaldehyde in alkaline medium. The compound formed from H-F and sodium nitroprusside in alkaline medium decomposes slowly in acid medium, in contrast to the behavior of methionine; the H-F decomposes at the same time. H-F gives absorption maxima in the McCarthy-Sullivan test at 430 and 490 m[mu] and interferes with the maximum at 510 m[mu] in the methionine determination. Homocysteine itself reduces the extinction value of sodium nitroprusside solution in the McCarthy-Sullivan reaction at 510 m[mu]. The reaction product from formaldehyde and excess homocysteine yields linear extinctions with sodium nitroprusside and small amounts of formaldehyde can be determined in this way. A modification of the McCarthy-Sullivan reaction is given which enables methionine and H-F to be determined together.