In vitro metabolism by turtle heart mitochondria

¹ Department of Biology, Saint Louis University, Saint Louis, Missouri

Both quantitative and qualitative aspects of the metabolic nature of heart mitochondria in the turtle, Chrysemys picta, have been investigated. Optimal in vitro incubation conditions for oxidative phosphorylation were approximated by alteration of the concentration of various components while using key substrates. The following has been established: exogenous cytochrome c is a necessary component; with an incubation volume of 2 ml the 2-µmole level of F^– is the most suitable; 40 µmoles P_i is requisite for substrates metabolized at a high rate; 10 µmoles Mg⁺⁺ is preferred with an initial ATP level of 3.2 µmoles. Succinate and malate were metabolized at similar rates (18 µmoles/mg N hr). Isocitrate was metabolized at about one-half this rate, whereas addition of NAD increased isocitrate oxidation to the succinate rate. -Ketoglutarate was utilized at nearly 2.5 times the rate of succinate. Pyruvate oxidation (roughly one-third the succinate rate) increased about ninefold upon addition of 1 µmole malate. ß-Hydroxybutyrate was metabolized at the same rate as succinate. Addition of 1 µmole malate increased this rate nearly fivefold. Citrate apparently was not metabolized. Theoretical P/O ratios were approached with all metabolized substrates. Short-term starvation caused a decrease in both oxidation and phosphorylation. The capacity of turtle heart mitochondria to metabolize intermediates of the tricarboxylic acid cycle appears to be equivalent to that of mitochondria of mammalian cardiac muscle heretofore published.

Key Words: oxidative phosphorylation • heart energy metabolism • poikilotherm metabolism • tricarboxylic acid cycle • oxidative metabolism • short-term starvation

Submitted on September 4, 1963