Past exam of the biochemistry and Molecular Biology course of the University of Cambridge / 2025 / Paper 2 / Section B / 12 / e / Solution

The mitochondrial dicarboxylate carrier is an inner-membrane transport protein that exchanges suitable dicarboxylates, including succinate and malate, with counter-substrates such as phosphate. In this experiment, it supplies external succinate to the matrix side of respiratory complex II; the inner mitochondrial membrane does not simply allow unrestricted diffusion of the charged substrate. Without adequate uptake, substrate delivery would restrict respiration even if the respiratory enzymes remained intact. Its essentiality is substrate- and preparation-dependent: it is not the obligatory entry route for every possible respiratory fuel.