Source:http://linkedlifedata.com/resource/umls/id/C1510421
GO: The gel-like material, with considerable fine structure, that lies in the matrix space, or lumen, of a mitochondrion. It contains the enzymes of the tricarboxylic acid cycle and, in some organisms, the enzymes concerned with fatty acid oxidation. [GOC:as, ISBN:0198506732],NCI: The area that is internal to the inner mitochondrial membrane.