Properties of a hemoglobin from the chromatrope of the nematode Mermis nigrescens.

The chromatrope pigment of Mermis nigrescens (Phylum: Aschelminthes, Class: Nematoda) was previously thought to have a role in photoreception. In this work it is shown to be an oxyhemoglobin whose absorption spectrum in vivo and in extracts resembles that of Ascaris oxyhemoglobins in having a weak alpha-band absorptivity. The extracted hemoglobin binds O2 and CO reversibly and with an affinity higher than that of the same concentration of horse hemoglobin. The Soret band of the deoxy derivative is unusually low and broad. Absorptivities and lambdamax for absorption bands of the oxy, deoxy and CO derivatives are tabulated for comparison with other hemoglobins. Microchemical procedures were developed which revealed that the chromatrope contains an average of 5-10(-12) mol of non-dialysable protoheme. Thus the hemoglobin concentration in the approx. 0.5 nl chromatrope volume is on the order of 10 mM (heme). The O2 binding ability and high in vivo concentration of this hemoglobin make possible a role in O2 storage or facilitation of O2 diffusion.