Ganglia of the marine bivalve, Saxidomus purpurata, are distinguished easily by red color from the surrounding tissues. The ganglia pigment with red color was soluble in water, and it was found to be composed of solely a hemoprotein by spectrophotometry. Spectral properties revealed that the hemoprotein resembles closely to that of mammalian hemoglobin in each case of the oxygenated-, carbonmonoxy- and acidic met-derivatives, but it differs strikingly in the deoxygenated-form. In the ganglia of Saxidomus, carotenoids which had been reported to be an important component of ganglia pigment were not detected. The micro-spectrophotometric and electron microscopic examinations made clear that the hemoprotein is localized in the granules which have been called cytosomes or lipochondria. The pigment granules were observed as spherical and electron dense organelle of about 1μm in diameter, and each of them was bounded by a unit membrane. The great majority of the granules occurred in the nerve cell bodies of a ganglion. Glycogen granules were often abundant in the vicinity of the pigment granules. Density of the granules was 1.05-1.07, so far as the estimation was made by a discontinuous density gradient ultracentrifugation of ganglia homogenate.
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