The biology of Asterias rubens L.V. A Porphyrin pigment in the integument

Abstract

A porphyrin pigment found in Asterias rubens has been re-examined and found to be protoporphyrin, and not haematoporphyrin as originally reported by MacMunn. The pigment was identified by spectroscopic and spectrophotometric observations as well as by chemical tests and the use of paper partition and column chromatography. The protoporphyrin is absent from the gut, gonads and digestive caeca, and is present only in' the leathery integument. The porphyrin occurs in the integument as free protoporphyrin; a yield of 33-6 mg. of red crystalline protoporphyrin dimethyl ester was obtained from a sample of 5485 g. of Asterias integument. The relative amounts of protoporphyrin in different coloured specimens of A. rubens were determined by a fluorimetric method. With four well-defined colour types the amount of porphyrin per gram of integument was found to decrease rapidly in the series: violet-brown, dark brown, red and pale. Neither protoporphyrin nor a porphyrinogen was found in the soft parts of Chlamys opercularis or Mytilus edulis, the main food animals of Asterias in the Plymouth area. The exact source of the integumentary porphyrin in this starfish is therefore uncertain, ,but it is suggested that it may be derived from the chlorophyll pigments found in the digestive caeca. The porphyrin does not contribute materially to the colour pattern of the animals, most of whose colour is carotenoid, and it is most likely that it is a by-product of excretion formed from chlorophyll.