The cristal membrane of mitochondria is the principal site of oxidative phosphorylation

TLDR

The mitochondrial inner membrane system consists of an inner boundary membrane adjacent to the outer membrane and a distinct cristal membrane forming tubules or lamellae inside. Immunolabeling and TEM of bovine heart tissue show that ~94 % of Complex III and ATP synthase reside in the cristal membrane, where their concentration is 2.2–2.6 fold higher than in the inner boundary membrane, supporting restricted diffusion and a specialized ATP‑producing compartment.

Abstract

The inner membrane system of mitochondria is known to consist of two contiguous but distinct membranes: the inner boundary membrane, which apposes the outer membrane, and the cristal membrane, which forms tubules or lamellae in the interior. Using immunolabeling and transmission electron microscopy of bovine heart tissue, we have calculated that around 94% of both Complex III of the respiratory chain and the ATP synthase are located in the cristal membrane, and only around 6% of either is in the inner boundary membrane. When accounting for the topographical ratio of cristal membrane versus inner boundary membrane, we find that both complexes exist at a 2.2–2.6‐fold higher concentration in the cristal membrane. The residual protein in the inner boundary membrane may be newly assembled complexes destined for cristal membranes. Our results argue for restricted diffusion of complexes through the cristal junctions and indicate that the mitochondrial cristae comprise a regulated submitochondrial compartment specialized for ATP production.