Functional differentiation of myoglobin isoforms in hypoxia-tolerant carp indicates tissue-specific protective roles

Abstract

Because of a recent whole genome duplication, the hypoxia-tolerant common carp and goldfish are the only vertebrates known to possess two myoglobin (Mb) paralogs. One of these, Mb1, occurs in oxidative muscle but also in several other tissues, including capillary endothelial cells, whereas the other, Mb2, is a unique isoform specific to brain neurons. To help understand the functional roles of these diverged isoforms in the tolerance to severe hypoxia in the carp, we have compared their O2 equilibria, carbon monoxide (CO) and O2 binding kinetics, thiol S-nitrosation, nitrite reductase activities, and peroxidase activities. Mb1 has O2 affinity and nitrite reductase activity comparable to most vertebrate muscle Mbs, consistent with established roles for Mbs in O2 storage/delivery and in maintaining nitric oxide (NO) homeostasis during hypoxia. Both Mb1 and Mb2 can be S-nitrosated to similar extent, but without oxygenation-linked allosteric control. When compared with Mb1, Mb2 displays faster O2 and CO kinetics, a lower O2 affinity, and is slower at converting nitrite into NO. Mb2 is therefore unlikely to be primarily involved in either O2 supply to mitochondria or the generation of NO from nitrite during hypoxia. However, Mb2 proved to be significantly faster at eliminating H2O2, a major in vivo reactive oxygen species (ROS), suggesting that this diverged Mb isoform may have a specific protective role against H2O2 in the carp brain. This property might be of particular significance during reoxygenation following extended periods of hypoxia, when production of H2O2 and other ROS is highest.

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

“…) and under anaerobic conditions as previously described (Shiva et al, 2007;Pedersen et al, 2010;Helbo et al, 2012). The nitrite concentration of freshly made stock solutions (~20mmoll -1 ) was verified by the Griess reaction (Giustarini et al, 2008) prior to experiments.…”

“…Varying amounts of nitrite was added anaerobically to the Mb solution via a Hamilton gastight syringe (Bonaduz, Switzerland) and spectral changes were measured over time in the range 390-650nm using an HP 8543 UVvis diode array spectrophotometer. At the end of the reaction, deoxy Mb (peak at 555nm) was fully converted to the Fe-NO form (peaks at 545 and 572nm) as predicted by the reaction stoichiometry (Shiva et al, 2007;Pedersen et al, 2010;Helbo et al, 2012). Observed rates (k obs ; s -1 ) were obtained by fitting absorbance traces at 555nm to single exponential decay functions.…”

“…It is not known, however, whether for Mbs a high O 2 affinity correlates with hypoxia tolerance and/or with a high nitrite reductase activity. Additionally, Mb can act as a peroxidase and scavenge hydrogen peroxide (H 2 O 2 ) (Yusa and Shikama, 1987;Flögel et al, 2004;Helbo et al, 2012), a major ROS produced endogenously when tissues are reoxygenated after hypoxia, thereby protecting against oxidative damage (Bickler and Buck, 2007;Flögel et al, 2004), as it would occur when whales reemerge from diving. Taken together, these enzymatic properties of Mb could contribute to the extreme tolerance to internal hypoxia displayed by whales during diving.…”

Ectopic Myoglobin Expression Is Associated with a Favourable Outcome in Head and Neck Squamous Cell Carcinoma Patients

“…Moreover, we assume that the potential beneficial effect of MB expression in cancer is independent from its primary respiratory functions, since the amount of MB protein expression would be too low to confer meaningful O 2 storage or buffering capacities (11). However, MB might play a scavenger role to support reduction of harmful ROS (5,22). In HNSCC, apart from mitochondrial processes, ROS are mainly produced by cigarette smoke; 86% of patients in our cohort have a documented smoking history.…”

Assessment of Commercial Quality Evaluation of Yellowfin Tuna Thunnus albacares Meat Based on Myoglobin Properties

“…Color is one of the most important factors affecting consumer preferences. The meat color of tuna is closely related with myoglobin (Mb) content and the red/ox state of the heme iron.Mb is a small globular protein whose biological function is basically to temporarily store oxygen in skeletal and cardiac muscles for facilitation of respiration (Livingston et al, 1983), though new functions of Mb have been recently reported, such as nitrogen oxide scavenging activity (Cossins and Berenbrink, 2008;Flögel et al, 2010;Helbo et al, 2012). Generally, Mb content changes dependent on animal species, muscle part, age, and diet of the animal.…”