The potentiating effect of purine bases and some of their derivatives on the oxygen affinity of haemocyanin from the crayfishAustropotamobius pallipes

Abstract

1. At pH 7.8 theP50 of dialysedAustropotamobius pallipes haemolymph (P50=1.7 Torr) was 2.9 Torr greater than that of nondialysed haemolymph (P50=4.6 Torr). This difference was not attributable to the specific effect ofl-lactate but rather to unidentified factors (U.F.) which increase the affinity of haemocyanin for oxygen. 2. The presence of 0.35 mM urate in the haemolymph of this species was confirmed as was the potentiating effect of this ion on oxygen affinity. In this study 2 mM urate reduced theP50 of dialysed haemolymph by approximately 50% from 4.6 Torr to 2.1 Toor. 3. The specificity of the haemocyanin for a specific purine structure was demonstrated to be low as the urate analogues, caffeine and theobromine, isolated from plants also increased the oxygen affinity of dialysed haemolymph. 4. Metabolites arising from the degradation of ADP/ATP to urate can also increase haemocyanin oxygen affinity to a variable extent but not as effectively as urate. Compounds in which the purine ring was cleaved evoked very little or no specific enhancement of haemocyanin oxygen affinity. 5. A combination of purine bases and derivatives, shown to produce individually an increase in oxygen affinity, did not produce an effect in excess of that due to urate alone. The presence of high concentrations of urate in the haemolymph abolishes the specific effect ofl-lactate. 6. Additive and synergistic effects ofl-lactate and the various purine derivatives may account for 80% of the U.F. effect.