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1‐Methyl‐4‐thiohistidine and Glutathione in the Developing Embryo of the Sea Urchin, Paracentrotus lividus.

4‐thiohistidines occur as free amino acids in the eggs of several marine organisms, in particulary relevant concentrations in the eggs of echinoderms. Since nothing is known about their biological role or biosynthesis and metabolic fate, we measured the concentration of 1‐methyl‐4‐thiohistidine together with the two most common small molecular weight thiols, glutathione and cysteine, during embryonic development of the sea urchin Paracentrotus lividus until the pluteus stage. The thiols were determined by high performance liquid chromatography as fluorescent derivatives of monobromobimanes. 1‐methyl‐4‐thiohistidine and glutathione are present until the pluteus stage with an approximate ratio of 2: 1. Cysteine was detected at the blastula stage and found to increase thereafter. 1‐methyl‐4‐thiohistidine was absent, or present in traces, in sperm and in somatic tissues of adults. It is concluded that 1‐methyl‐4‐thiohistidine is typical of eggs and embryos and may be metabolized during metamorphosis into an as yet unknown compound.