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THE CO 2 SENSITIVITY OF THE HEMOCYANINS AND ITS RELATIONSHIP TO Cl - SENSITIVITY

1986; Marine Biological Laboratory (MBL); Volume: 171; Issue: 1 Linguagem: Inglês

10.2307/1541921

1939-8697

Charlotte P. Mangum, Louis E. Burnett,

Neurobiology and Insect Physiology Research

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 the pairing of the allosteric effectors Ca+2 and Mg+2 with the CO2 anions. In contrast the effect of CO2 on crustacean hemocyanins is greaterat 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 a influences only oxygen affinity, CO2 may influence cooperativity as well. Indifferent species the effects of both Cl- and CO2 may or may not be great enough to be physiologically important.