Cleaving embryos of the sea urchin Paracentrotus lividus exposed briefly to buffered saline release materials into the medium which will bleach a yellow mixture of DTNB and DTT [5,5'-dithiobis (2-nitrobenzoic acid) and dithiothreitol]. The decolorant activity is thermolabile and dialysable. The bleached mixture recolors rapidly on heating, suggesting the breakdown of a complex between the decolorant and the yellow DTNB ion.

The release of decolorants is maximal at the blastula stage, and in Ca-free saline, Tris-HCl pH 7. When various untreated embryonic stages are homogenized with DTNB, the assay for SH is lowest at blastula, suggesting that decolorants in the blastulae interfere with the assay.

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