THE SPONTANEOUS HEMIN RELEASE FROM LUMBRICUS-TERRESTRIS HEMOGLOBIN

The slow, spontaneous release of hemin from earthworm, Lumbricus terre stris, hemoglobin has been studied under mild conditions in the presen ce of excess apomyoglobin. This important protein is surprisingly unst able. The reaction is best described as hemin released from the globin into water, followed by quick engulfment by apomyoglobin. The energet ics of this reaction are compared with those of other types of hemoglo bins. Anomalously low activation energy and enthalpy are counterbalanc ed by a negative entropy. These values reflect significant low frequen cy protein motion and dynamics of earthworm hemoglobin and may also in dicate an open structure distal to the heme. This is also supported by the infrared spectrum of the carbonyl hemoprotein, which indicates se veral types of distal interactions with the bound CO. The reported low heme to polypeptide ratio for this protein may be due to facile heme and hemin release by the circulating protein. (C) 1997 Elsevier Scienc e Inc.