Mitochondria matrix contains soluble enzymes in the cell that is used as some sort of catalyst in the process of oxidation. Inside the matrix, it also contains the components of the mitochondria's DNA and also its ribosomes. A electron transport chain takes place in the matrix. The reactants produced by the citric acid cycle reaction releases a proton and also an electron to regenerate positive electron charges.
The matrix contains the enzymes that are responsible for the citric acid cycle reaction, it also contains dissolved oxygen, water, carbon dioxide, the recyclable intermediates that serve as energy shuttles