The protein components of the isolated myofibril.

5. Specimens from Prof. C. J. Watson's laboratory have been examined. The uroporphyrin methyl ester I had m.p. 292-293° and behaved as uroporphyrin I containing a trace of uroporphyrin III on paper chromatography. The 2080 ester behaved chromatographically as a hexacarboxylic porphyrin. We wish to thank Dr Falk and Miss Benson for performing the chromatographic examinations by their method, and also Prof. C. J. Watson and Dr J. Canivet for kindly placing materials at our disposal. A generous grant to one of us (C. R.) from the Trustees of the Nuffield Foundation has made possible the establishment ofa Unit for the Investigation of Pyrrole Pigment Metabolism and this grant is gratefully acknowledged.