Mitochondrial matrix
The cytosolic, intermembrane space, compartment has a water content of 3.8 μl/mg protein, while the mitochondrial matrix 0.8 μl/mg protein. It is not known how mitochondria maintain osmotic balance across the inner mitochondrial membrane, although the membrane contains aquaporins that are believed to be conduits for regulated water transport. Mitochondrial matrix has a pH of about 7.8. Mitochondrial DNA was discovered by Nash and Margit in 1963. One to many double stranded mainly circular DNA is present in mitochondrial matrix. Mitochondrial DNA is 1% of total DNA of a cell. It is rich in Guanine and Cytosine content. Mitochondria of mammals have 55s ribosomes.
Denisovan
The mitochondrial DNA (mtDNA) from the finger bone discovered in Denisova Cave differs from that of modern humans by 385 bases (nucleotides) out of approximately 16,500, whereas the difference between modern humans and Neanderthals is around 202 bases. In contrast, the difference between chimpanzees and modern humans is approximately 1,462 mtDNA base pairs. This suggested a divergence time around one million years ago. The more divergent Denisovan mtDNA has been interpreted as evidence of admixture between Denisovans and an unknown archaic population. Studies suggest that a population related to modern humans contributed mtDNA to the Neanderthal lineage, but not to the Denisovan mitochondrial genomes yet sequenced. It has suggested the species could be "Homo heidelbergensis", but that species is now generally considered to be too closely related to the Neanderthals. That it could have been a "Homo erectus"-like introgression into the Denisovans about 53,000 years ago that is responsible for the anomalously-divergent mtDNA has also been proposed.