ERYTHROCRUORIN OF MARPHYSA SANGUINEA.

1. The polychaete worm Marphysa sanguinea has a circulating erythrocruorin of mol.wt. about 2.4x10(6) (S(0) (20,w) 58.2s, D(20,w) 2.06x10(-7) cm.(2)/sec). This is the predominant form existing at pH 6-8 and (non-protein) I 0.10-0.21, and also at approx. pH 6.7 and I 0.15-3.00. 2. The pigment contains 2.24% of protohaem. 3. The 58s protein has an electrophoretic mobility of 8.08x10(-5) cm.(2)/v/sec. at pH 8.12, I 0.21 and 0 degrees . The isoelectric point of suspended particles is 4.63 at I 0.16 and 21.5 degrees . 4. At very low ionic strength and pH 6.7 (unbuffered) the 58s pigment associates reversibly to 97s and 150s forms, which are probably dimer and tetramer species. 5. At pH 10.0 and I 0.025, it dissociates irreversibly to give a small amount of 2-4s non-haem-containing protein and much 9s haem-enriched protein. These and the 58s pigment may correspond to structures found in Levin's (1963) electron-microscope studies of other erythrocruorins. 6. Absorption spectra of the 58s oxygenated erythrocruorin and the deoxygenated and carbon monoxide derivatives have been obtained.