Ovohemerythrin, a major 14-kDa yolk protein distinct from vitellogenin in leech

A 14-kDa protein was identified as a major component of mature oocytes of the leech Theromyzon tessulatum. This protein was, like vitellin, detected in the content of yolk granules and was purified by gel-permeation and ion-exchange chromatography. The yolk protein corresponded to an iron-binding protein which exists in a monomeric unglycosylated form and had no similarities to vitellin. However, a strong resemblance between this protein and sipunculid hemerythrin, a non-heme iron-binding protein, was observed on the basis of its characteristics including molecular mass, iron content, ultraviolet/visible spectrum, amino acid composition and N-terminal sequence. These similarities with hemerythrin and the accumulation of the protein in the oocyte justify the name ovohemerythrin given to the molecule. A coelomic-fluid protein immunologically related to ovohemerythrin was detected in vitellogenic animals. The protein was purified with the chromatographic procedure used to isolate ovohemerythrin from oocytes and was found to be similar to the oocyte protein. This circulating ovohemerythrin was present in large amounts in the coelomic fluid while gametogenesis is in progress, i.e. after the third and last blood meal of the animal (stage 3), except at the time of oocyte enlargement when its concentration decreases dramatically. However, in contrast to vitellogenin, which is detected specifically in the coelomic fluid of leeches at stage 3, circulating ovohemerythrin is also observed after the first (stage 1) and second (stage 2) blood meal. This observation suggests a more complex function for ovohemerythrin than being merely a yolk nutrient for the embryo.