The reaction between thiobarbituric acid and the oxidation products of certain lipides.

In 1944 Kohn and Liversedge (1) showed that tissue suspensions or slices incubated aerobically produce a compound which will condense with either p-aminobenzoic acid (PAB) to give a yellow color or with thiobarbituric acid to give an orange-red color. Brain is the most active tissue, liver next, and other tissues show some activity. Subsequently, Bernheim et al. (2) found that washed brain suspension boiled for 10 minutes and then incubated aerobically with small amounts of ascorbic acid takes up oxygen and produces the substance which condenses with PAB or thiobarbituric acid. Apparently, in the presence of ascorbic acid something is split from the brain protein. Elliott and Libet (3) have shown that phospholipides increase the oxygen uptake of brain suspensions and that this effect is increased by ascorbic acid. Accordingly, we prepared and purified lecithin from brain. and also from eggs, and, after incubating this lecithin with ascorbic acid, obtained colors with PAB and thiobarbituric acid. The absorption spectra of both are identical with those reported by Kohn and Liversedge. It thus seems that ascorbic acid catalyzes the oxidation of lecithin, either free or combined with tissue protein, and that this oxidation can be followed quantitatively by the use of either one of the reagents