THE CO2SENSITIVITY OF THE HEMOCYANINS AND ITS RELATIONSHIP TO Cl-SENSITIVITY

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Abstract
The effect of CO2 on hemocyanin-oxygen binding is not generally related to the effect of Cl-. Some hemocyanins respond to both and some to either one alone. The direction of the responses of O2 affinity of the various hemocyanins to CO2 is poorly correlated with the direction of responses to other effectors. The influence of CO2 on Busycon and Limulus hemocyanins reaches its maximum at high pH. Since the effect can be abolished by restoring divalent cation activities to the control levels prior to the addition of CO2, we suggest that the effect is not specific but rather indirect, by pairing of the allosteric effectors Ca+2 and Mg+2 with the CO2 anions. In contrast the effect of CO2 on crustacean hemocyanins is greater at low pH and it can be enhanced by maintaining HCO3- levels within narrow limits and permitting PCO2 to vary by a large factor. This finding suggests that the effective species is molecular CO2. While Cl- influences only oxygen affinity, CO2 may influence cooperativity as well. In different species the effects of both Cl- and CO2 may or may not be great enough to be physiologically important.