Department of Biological Sciences

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Browsing Department of Biological Sciences by Author "Patel, Suchita"

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    Characterization of the oxygen binding properties of hemoglobin from the ruby-throated hummingbird (Archilochus colubris)
    (2024-07-04) Patel, Suchita; Signore, Anthony (Biological Sciences); Fraser, Kevin (Biological Sciences); Campbell, Kevin
    Weighing only between 2.5 and 4.8 g, the ruby-throated hummingbird (A. colubris) has one of the highest known mass-specific metabolic rates among birds. Despite this, there is a lack of available data on the oxygen binding properties of their hemoglobin (Hb). Here I measured the effect of allosteric effectors, pH and temperature on the O2-affinity (defined as the O2 partial pressure required for 50% Hb O2 saturation; P50) of ruby-throated hummingbird Hb, while also estimating their Hb buffering capacity. A comparison of Hb-O2 affinity (i.e. P50 values) between A. colubris and its sole congener, the black-chinned hummingbird (A. alexandri), revealed differences likely attributed to two β-chain amino acid substitutions. Under treatment conditions resembling the natural physiological state of hummingbird blood, A. colubris exhibited a similar Bohr effect (-0.401) and buffering capacity (4.88 mol H+ mol Hb4-1 pH-1) to those of other hummingbird species, though both variables were among the lowest values previously reported for birds. Nonetheless, the low buffering capacity is modelled to enhance the efficiency of their (relatively low) Bohr effect and may enable a high blood [Hb], which together with a relatively low blood O2 affinity is shown to markedly increase tissue O2 delivery. I also found that O2 binding of A. colubris Hb was thermally insensitive under natural physiological conditions. This thermal insensitivity could help ensure adequate O2 delivery both during and upon arising from torpor, while minimize heat loss at the lungs. These findings highlight the various O2 binding properties of A. colubris that together facilitate the efficient delivery of O2 to the tissues irrespective of temperature.