Pyrimidines · reaction 4 of 6

Dihydroorotate + Ubiquinone → Orotate + Ubiquinol

Dihydroorotate dehydrogenase EC 1.3.5.2

The only enzyme of the pathway that is not in the cytosol: it sits on the inner membrane of the mitochondrion and hands its electrons directly to the ubiquinone of the respiratory chain.

irreversible
Inner mitochondrial membrane

in depth

ΔG°′: not documented
Location: Inner mitochondrial membrane

Fun fact

That is why making pyrimidines depends on respiration working. A cell without an active respiratory chain cannot make new DNA even if it has energy to spare from other sources.

Nelson, D. L. & Cox, M. M. (2021). Lehninger. Principios de bioquímica, 8.ª ed., ch. 22

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PyrimidinesDihydroorotate dehydrogenase

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