Haemocyanin function in the New Zealand abalones Haliotis iris and H. australis: relationships between oxygen-binding properties, muscle metabolism and habitat

Abstract

Abalone have a well developed capacity for anaerobic metabolism in the pedal musculature, and during exercise the haemolymph oxygen stores may be reserved for more oxygen-dependent tissues. This implies that the haemocyanin-based oxygen transport system is poised towards oxygen storage rather than high rates of oxygen delivery. This proposition was examined by determining O₂ -binding properties of haemocyanin from two species of abalone that differ in behaviour and environmental oxygen requirements. Both species showed reversed Bohr and Root effects leading to very high oxygen affinity and reduced cooperativity at low pH. A marked temperature sensitivity of haemocyanin–O₂ binding in H. iris (with heat of oxygenation at –55.7 kJ mol^-1) impairs oxygen loading above 20˚C and may explain the reduced size and density of populations in warmer northern waters. Muscle enzyme activities indicate low maximum rates of ATP production, with arginine phosphate hydrolysis as the primary source of ATP for elevated levels of muscle work. These data support the hypothesis that oxygen stores support high levels of aerobic muscle work. However, the similarities in enzyme profiles and haemocyanin properties could not be related to behavioural and habitat differences.