Oxygen-binding modulation of hemocyanin from the slipper lobster Scyllarides latus.
The oxygen-binding properties of hexameric hemocyanin (Hc) from Scyllarides latus were investigated with respect to pH, temperature, and modulating effect exerted by calcium, lactate, and urate. The oxygen affinity decreased at higher temperature, was slightly affected by pH, and was insensitive to lactate. Nevertheless, urate markedly increased Hc-oxygen affinity and its temperature sensitivity, acting as the physiological major positive effector: four urate sites per hexamer with an overall affinity constant of 1 x 10(4) M(-1) were found and the exothermic contribution of their binding was found to be about 30 kJ mol(-1). Calcium ions largely influenced oxygen affinity: their effect, which has an opposite sign at low (0-1 mM) and high (0.1-1 M) concentration ranges, indicates the presence of two independent types of binding sites with high and low affinity, respectively; however, only the former ones seem to be operative in vivo because, at physiological calcium concentrations, they are already saturated and the oxygen affinity is reduced.
Sanna
Maria T
MT
Department of Sciences Applied to Biosystems, University of Cagliari, Cittadella Universitaria, Monserrato I-09042, CA, Italy.
Olianas
Alessandra
A
Castagnola
Massimo
M
Sollai
Luigi
L
Manconi
Barbara
B
Salvadori
Susanna
S
Giardina
Bruno
B
Pellegrini
Mariagiuseppina
M
D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D002118:Calcium / Q000494:pharmacology; D033364:Decapoda / Q000378:metabolism*; D006433:Hemocyanins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000494:pharmacology; D010100:Oxygen / Q000378:metabolism*; D013696:Temperature; D014527:Uric Acid / Q000494:pharmacology
D014527:Uric Acid; D019344:Lactic Acid; D006433:Hemocyanins; D010100:Oxygen; D002118:Calcium