Meeting Abstract
P3.87 Thursday, Jan. 6 Enzymatic flux capacities in hummingbird flight muscles: A “One Size Fits All” Hypothesis FERNANDEZ, MJ*; SUAREZ, RK; Univ. of North Carolina, Chapel Hill; Univ. of California, Santa Barbara mjfernan@email.unc.edu
Among vertebrates, hummingbirds are unique in their capacity for sustained hovering. Given the allometric scaling of hovering metabolic rates among hummingbird species, we hypothesized mass-dependent variation in enzymatic flux capacities (Vmax values) of key enzymes in pathways of glucose and fatty acid oxidation in the flight muscles. We obtained data from four species ranging in body mass from 4 to 20 grams, covering 88% of the entire range of body mass variation among hummingbirds. Because flight muscles account for most of the VO2 during hovering flight, we were able to accurately estimate metabolic flux rates from respirometric data obtained during hovering flight. Our results reveal that hummingbirds share a highly conserved set of pathways for glucose and fatty acid oxidation. In addition, there was a lack of quantitative, mass-dependent interspecific variation in Vmax values for most of the enzymes involved in glucose and fat oxidation. These results suggest a “one size fits all” hypothesis, i.e., qualitative as well as quantitative evolutionary conservation of pathways of energy metabolism. The lack of correlation between Vmax values and flux rates at most steps in energy metabolism, suggests that the interspecific variation in flux through pathways of glucose and fatty acid oxidation during hovering is achieved through modulation of enzyme activities, rather than adjustments in enzyme concentration. This is discussed in terms of hierarchical regulation analysis (ter Kuile and Westerhoff, 2001), as previously applied to interspecific variation in flight metabolic rates by Suarez et al. (2005).
