Hemocyanin Subunit Composition and Oxygen Binding in Two Species of the Lobster Genus Homarus and Their Hybrids

The monomeric subunit composition and O2 binding properties of the hemocyanins (Hcs) of Homarus americanus, H. gammarus and their hybrids are very similar, though not identical. H. americanus Hc has six major electrophoretically separable polypeptide chains; H. gammarus Hc has four major and two minor chains; and the hybrid Hc has four major and one minor chain. Four chains co-migrate in all three groups, and the fifth chain in the hybrid co-migrates with a fifth chain in H. gammarus. Thus, qualitatively, the hybrid Hc is more like that of H. gammarus than H. americanus, a similarity reflected in respiratory properties. Although the O2 affinity of the hybrid hemocyanin appears to lie intermediate between that of the two parent hemocyanins at 25°C, in fact it is significantly different from that of H. americanus but not H. gammarus. The cooperativity of the hybrid Hc also differs significantly from that of H. americanus but not H. gammarus Hc. The distinctive properties of H. americanus hemocyanin at 25°C are believed to be due to either or both of two chains: a unique and also invariant chain in H. americanus, and one that is present in H. gammarus and the hybrids but not in H. americanus. H. americanus Hc also appears to be slightly less sensitive to the allosteric modulator L-lactate. No difference in CaCl2 sensitivity was found. At lower temperatures respiratory properties are indistinguishable. In adult H. americanus that had been held under identical conditions for long periods, variation in subunit pattern was not entirely absent, but it was smaller than that found in natural populations of other species. No differences in O2 binding at 25°C were found in morphs differing qualitatively in one chain and quantitatively in two others. No effect of a combination of rearing temperature and diet was found on the Hc subunit composition of juveniles.