Oxygen equilibrium and subunit aggregation of a holothurian hemoglobin.

The hemoglobin of the sea cucumber Cucumaria miniata Brandt has a mol. wt of about 36000 in the oxy- form with a s20,w equal to 2.9 and a subunit molecular weight of 18000 by sodium dodecylsulfate gel electrophoresis. This pigment aggregates when deoxygenated to an oligomer with a s20,w equal to 4.7, an aggregation which is reversible upon subsequent oxygenation. The hemoglobin shows a sigmoid binding equilibrium with "n" equal to 1.8 and a decrease in oxygen affinity with an increase in pigment concentration. This hemoglobin is compared with other hemoglobins showing oxygenation-linked subunit aggregation.