Mitochondrial substrate specificity in beetle flight muscle: assessing respiratory oxygen flux in small samples from Dermestes maculatus and Tenebrio molitor

In the present study, the permeabilized fibre approach is adapted to investigate substrate utilization patterns in the flight muscle mitochondria of Dermestes maculatus (Coleoptera: Dermestidae; a carrion scavenger beetle) and Tenebrio molitor (Coleoptera: Tenehrionidae; a phytophagous scavenger beetle). Respiration in saponin-permeabilized fibres is measured during titration of palmitoyl-carnitine (Palm-C), pyruvate (Pyr) or L-glycerol 3-phosphate (G3-P), Michaelis-Menten-type enzyme kinetics for oxygen consumption arc observed as a function of substrate concentration in Pyr and G3-P, from which substrate-specific apparent K-m (sensitivity) and V-max (capacity) are determined. Compared with D. maculatus, the apparent K-m in T. molitor is lower (P < 0.001) for Pyr, and V-max is greater for G3-P (P < 0.001). In D. maculatus, the apparent K-m for G3-P is greater (P < 0.001), and respiratory V-max is lower (P < 0.001), than kinetics for Pyr. Robust respiration with L-proline (Pro) is also observed in both beetle species tested; however, it is over 2.5-fold greater in D. maculatus than T. molitor (P < 0.05). These results demonstrate that respiration in beetle flight muscle mitochondria can be assessed in small samples (i.e. at the individual beetle level) using the approach adapted for the present study. The results of the present study also highlight the substrate oxidative capacity patterns in both D. maculatus and T molitor, which rank Palm-C < G3-P < Pyr < Pro.