Design of Oxidative Capacities in Hymenopteran Flight Muscles

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

Flying insects achieve the highest known mass-specific rates of aerobic metabolism in the Animal Kingdom. How these high metabolic flux rates are achieved to support flight is poorly understood. During flight, steady state rates of mechanical work define rates of ATP hydrolysis and resynthesis. The applicant asks how capacities for ATP synthesis are related to ATP requirements for flight. In previous studies using honeybees (Apis mellifera), the applicant found remarkably close matches between enzymatic capacities for glycolysis and glycolytic rates achieved during flight. As an extension of these studies, further research will be conducted to determine how closely mitochondrial oxidative capacities match requirements during flight. An important question is whether honeybee flight muscle mitochondria possess inherently higher capacities for respiration and oxidative phosphorylation than mitochondria from vertebrate homeotherm muscles. Honeybee mitochondria will be isolated and characterized to determine how oxidative capacities are related to the respiration rates achieved in flight. Further studies to investigate the basis for high respiration rates in honeybees will involve mechanistic studies of electron transfer reactions in isolated muscle mitochondria. The relationships between biochemical capacities and physiological flux rates will be further explored in a comparative study using various species of Euglossine (orchid) bees, which vary greatly in size and are known to display an inverse relationship between body mass and mass-specific metabolic rate during flight. It is proposed that in Euglossine bees, the inverse relationship between body mass and mass-specific aerobic metabolic rate is achieved partly through variation in mitochondrial content and structure, as well as higher enzyme turnover rates (electron transfer rate per enzyme molecule) with declining body mass. These unique studies will shed light upon how metabolic enzymes function in vivo and the principles governing the design of biochemical capacities. The rules that govern how much enzyme is "enough but not too much" are poorly understood. The applicant's research program is based on the belief that progress towards this goal is of fundamental importance to biology.