Cloning and analysis of the gene encoding hummingbird proinsulin

Because hummingbirds exhibit the highest mass-specific metabolic rates seen among vertebrates and rely on sugars as their main energy source, we have investigated the structure of hummingbird insulin (Selaphorus rufus) to determine whether it possesses structural adaptations that increase its receptor binding affinity (potency). We report here the nucleotide sequence of hummingbird proinsulin determined from hummingbird genomic DNA. The predicted amino acid sequence of the A-chain of hummingbird insulin is identical to that of chickens and the B-chain differs by only one amino acid at a noncritical position, B2 (Val in hummingbird and Ala in chicken). These findings suggest that alterations in secretory and metabolic dynamics of insulin are of greater importance than changes in binding affinity in the adaptation to states of high carbohydrate flux in these very energetic organisms.