The extracellular products of Anabaena cylindrica Lemm. II. Fluorescent substances containing serine and threonine,and their role in extracellular pigment formation

From aged-culture filtrates of Anabaena cylindrica Lemm., two similar compounds were isolated which fluoresced strongly in ultraviolet light. Hydrolysis of each gave a single different fluorescent moiety, and serine and threonine in a probable ratio of 2 : 1. No carboxy- or amino-terminal amino acid was present. On chromatograms exposed to light, the fluorescent peptides turned yellow-brown. Analysis of the results of this reaction indicated conversion to similar but yellow substances, followed by polymerisation to give a macromolecular brown pigment-peptide, indistinguishable from a similar complex which represents a major extracellular product of the alga.