O-Methylthreonine, a New Bleaching Agent for Euglena gracilis

SUMMARY: O-Methylthreonine (OM) inhibits multiplication and photosynthetic pigment synthesis in Euglena gracilis and Ochromonas danica; it does not inhibit Chlamydomonas reinhardi or Rhodopseudomonas palustris. Inhibition of multiplication and pigment synthesis may be prevented by l-isoleucine. OM also causes the permanent loss of chlorophyll and appreciable loss of carotenoids in E. gracilis and this may be prevented by l-isoleucine, α-aminobutyric acid, α-ketobutyric acid, l-threonine, l-homoserine, or l-methionine. α-Ketobutyric acid is most effective on a molar basis and is therefore postulated to be the target of OM inhibition. Isoleucine plays a role in the biosynthesis of photosynthetic pigments and lipids in Euglena gracilis, for the incorporation of 14C-l-isoleucine radioactivity into both the pigments and lipids is markedly diminished by bleaching agents which prevent pigment synthesis without affecting multiplication, i.e. O-methylthreonine or streptomycin. When pigment synthesis is blocked amino acids accumulate in the culture supernate.