Functional properties of myoglobins from five whale species with different diving capacities

Whales show an exceptionally wide range of diving capabilities and many express high amounts of the O-2 carrier protein myoglobin (Mb) in their muscle tissues, which increases their aerobic diving capacity. Although previous studies have mainly focused on the muscle Mb concentration and O-2 carrying capacity as markers of diving behavior in whales, it still remains unexplored whether whale Mbs differ in their O-2 affinities and nitrite reductase and peroxidase enzymatic activities, all functions that could contribute to differences in diving capacities. In this study, we have measured the functional properties of purified Mbs from five toothed whales and two baleen whales and have examined their correlation with average dive duration. Results showed that some variation in functional properties exists among whale Mbs, with toothed whale Mbs having higher O-2 affinities and nitrite reductase activities (similar to those of horse Mb) compared with baleen whale Mbs. However, these differences did not correlate with average dive duration. Instead, a significant correlation was found between whale Mb concentration and average duration and depth of dives, and between O-2 affinity and nitrite reductase activity when including horse Mb. Despite the fact that the functional properties showed little species-specific differences in vitro, they may still contribute to enhancing diving capacity as a result of the increased muscle Mb concentration found in extreme divers. In conclusion, Mb concentration rather than specific functional reactivities may support whale diving performance.