ONTOGENY OF HEMOCYANIN FUNCTION IN THE DUNGENESS CRAB CANCER-MAGISTER- THE INTERACTIVE EFFECTS OF DEVELOPMENTAL STAGE AND DIVALENT-CATIONSON HEMOCYANIN OXYGENATION PROPERTIES

Calcium and magnesium ions raise the oxygen affinities of 25S hemocyan ins of both first-instar juvenile and adult Cancer magister. A physiol ogically relevant change in magnesium concentration from 16 to 32 mmol l-1 changes first-instar juvenile hemocyanin affinity by 5.6 mmHg (0. 7kPa) but adult affinity by only 1.1 mmHg (0. 15kPa). In early juvenil e crabs, the higher magnesium sensitivity of the hemocyanin may be com pensated for by the lower oxygen affinity, which has been shown previo usly to be 50% lower than that of the adult under identical experiment al conditions. Furthermore, ontogeny of ionic and osmotic regulation o ccurs during the development of C. magister, with especially high conc entrations of magnesium being found in the hemolymph of early juvenile s. Intermediate-stage juveniles (fifth to eighth instars) have hemocya nins with subunit stoichiometries and P50 Values approaching those of the adult. These findings are significant because they indicate that m odulation of C. magister hemocyanin oxygen-affinity during development incorporates differences in intrinsic affinity and differences in div alent cation sensitivity of the stage-specific hemocyanins.