. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SULFUR METABOLISM IN ARENICOLA 365 from cysteine to sulfate is through transamination between cysteinesulfinic acid and a-ketoglutaric acid to form glutamic acid and an unstable intermediate, /8-sulfinylpyruvic acid. The latter decomposes into sulfite, which is oxidized to sulfate, and into pyruvic acid, which by transamination with glutamic acid re- generates a-ketoglutaric acid and forms alanine. It has been demonstrated that both enzymatic and non-enzymatic oxidation of sulfite to sulfate occur in mammals (Heimberg, Frido
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SULFUR METABOLISM IN ARENICOLA 365 from cysteine to sulfate is through transamination between cysteinesulfinic acid and a-ketoglutaric acid to form glutamic acid and an unstable intermediate, /8-sulfinylpyruvic acid. The latter decomposes into sulfite, which is oxidized to sulfate, and into pyruvic acid, which by transamination with glutamic acid re- generates a-ketoglutaric acid and forms alanine. It has been demonstrated that both enzymatic and non-enzymatic oxidation of sulfite to sulfate occur in mammals (Heimberg, Fridovich and Handler, 1953; Fridovich and Handler, 1956). The enzymatic process is heat-labile. When sodium sulfite solutions were incubated with the soluble enzyme preparations from A. cristata, the results in terms of sulfite remaining after one hour, although some- what erratic, indicated that no decrease in activity was effected by boiling the enzyme preparation. Thus, the enzymatic mechanism may be of little importance in Arcnicola, or mar be absent. 3000-30 i. 3i 1 52000-20^ o o 1000 o RADIOACTIVITY • ACIDIC COMPOUNDS CYSTEINE SULFINIC ACID o. - 20 40 FRACTION NUMBER 50 60 FIGURE 2. Acidic components from 1 gm. of Arcnicola cristata 12 hours after injection of S^-cysteine. Fractions are 1-ml. portions of eluate from 60 X cm. Dowex 50 (H+) column. The activity of the cysteinesulfinic acid-a-ketoglutaric acid transaminase system in vitro may be evaluated from Table VI, which presents the most consistent series of experimental results obtained in several trials of this system. The values reported for glutamic acid represent increases above the endogenous level for this substance. There seems little reason to doubt the formation of sulfate via the transaminase-^-sulfinylpyruvate pathway. The formation of hypotaurine in the mammal by decarboxylation of cysteine- sulfinic acid has been established for some time (Bergeret and Chatagner, 1952; Bergeret, Chatagner and Fromag
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