ONTOGENY OF HEMOCYANIN FUNCTION IN THE DUNGENESS CRAB CANCER-MAGISTER- HEMOLYMPH MODULATION OF HEMOCYANIN OXYGEN-BINDING

The in vivo oxygen-binding characteristics of Cancer magister whole he molymph were compared across developmental stages with those of purifi ed hemocyanin. When the 25S hemocyanins from first-instar juvenile and adult C. magister were dialyzed against first-instar juvenile saline, the P-50 values at pH 7.8 differed by 54%: 2.16 kPa for the adult and 4.68 kPa for the first-instar juvenile. Since both purified proteins were examined under identical conditions, this represents an intrinsic stage-specific difference in hemocyanin O-2-affinity. When the two ty pes of hemocyanin were dialyzed against their respective stage-specifi c salines, the oxygen affinities differed by only 28%: 3.39 kPa for th e adult and still 4.68 kPa for the first-instar juvenile. Thus, the in trinsic difference in hemocyanin O-2-affinity was reduced by the stage -specific differences in hemolymph ion concentrations, Even more signi ficant is the fact that the whole-hemolymph P-50 values of the juvenil e and adult were indistinguishable at in vivo pH and divalent cation l evels specific for each stage, Thus, despite significant differences i n the intrinsic oxygen affinity of the purified 25S hemocyanin during development, the whole-hemolymph oxygen-binding properties are conserv ed. In the juvenile crab, it appears that the low-affinity hemocyanin serves to modulate the effects of a weak renal regulation of [Mg2+]. A s ion regulation is enhanced during development and divalent cation le vels decrease, the crab synthesizes higher-affinity hemocyanin.