HEMOCYANIN OXYGEN-BINDING PROPERTIES OF A DEEP-SEA HYDROTHERMAL VENT SHRIMP - EVIDENCE FOR A NOVEL COFACTOR

Rimicaris exoculata is a caridean shrimp from the family Alvinocaridid ae which forms the dominant species around deep-sea hydrothermal vents from the Mid-Atlantic Ridge (MAR). Seeking respiratory adaptations to the hydrothermal environment, we have analysed the oxygen-binding pro perties of Rimicaris hemocyanin (Hc) in relation with temperature, pH, and lactate variations. Rimicaris native Hc is mostly composed of hex amers. It showed a high oxygen affinity (P-50 approximately 3 Torr at pH 7.5, 15 degrees C), a large Bohr effect (Delta logP(50)/Delta pH = 1-1.87 +/- 0.25, n = 6), a moderate lactate effect (Delta logP(50)/Del ta log[lac] = -0.12) and almost no temperature effect (Delta H = -1.23 kJ.mol(-1) 15-35 degrees C). Most surprisingly, dialysis of native he molymph elicited a large increase of Hc-O-2 affinity, an effect opposi te to the usual trend observed for crustacean Hcs. Moreover, this incr ease in affinity could be reversed by adding an ultrafiltrate of nativ e hemolymph to a dialysed sample, thus unveiling the existence of a di alysable yet unknown cofactor which decreases Hc-oxygen affinity. (C) 1997 Wiley-Liss, Inc.