Editing Adenosine triphosphate (section)

====Beta oxidation====
{{Main|Beta-oxidation}}
In the presence of air and various cofactors and enzymes, fatty acids are converted to [[acetyl-CoA]]. The pathway is called [[beta-oxidation]]. Each cycle of beta-oxidation shortens the fatty acid chain by two carbon atoms and produces one equivalent each of acetyl-CoA, NADH, and FADH<sub>2</sub>. The acetyl-CoA is metabolized by the citric acid cycle to generate ATP, while the NADH and FADH<sub>2</sub> are used  by oxidative phosphorylation to generate ATP.  Dozens of ATP equivalents are generated by the beta-oxidation of a single long acyl chain.<ref>{{cite journal |last1=Ronnett |first1=G. |last2=Kim |first2=E. |last3=Landree |first3=L. |last4=Tu |first4=Y. | title = Fatty acid metabolism as a target for obesity treatment | journal = Physiol. Behav. | volume = 85 | issue = 1 | pages = 25–35 | year = 2005 | pmid = 15878185 | doi=10.1016/j.physbeh.2005.04.014 |s2cid=24865576 }}</ref>

=====Regulation=====
In oxidative phosphorylation, the key control point is the reaction catalyzed by [[cytochrome c oxidase]], which is regulated by the availability of its substrate&nbsp;– the reduced form of [[cytochrome c]]. The amount of reduced cytochrome c available is directly related to the amounts of other substrates:

:<math chem="">
\frac12 \ce{NADH} + \ce{cyt}\ \ce{c_{ox}} + \ce{ADP} + \ce{P_{i}} \rightleftharpoons
\frac12 \ce{NAD^+} + \ce{cyt}\ \ce{c_{red}} + \ce{ATP}
</math>

which directly implies this equation:

:<math>
\frac{[\mathrm{cyt~c_{red}}]}{[\mathrm{cyt~c_{ox}}]} = \left(\frac{[\mathrm{NADH}]}{[\mathrm{NAD}]^{+}}\right)^{\frac{1}{2}}\left(\frac{[\mathrm{ADP}] [\mathrm{P_i}]}{[\mathrm{ATP}]}\right)K_\mathrm{eq}
</math>

Thus, a high ratio of [NADH] to [NAD<sup>+</sup>] or a high ratio of [ADP] [P<sub>i</sub>] to [ATP] imply a high amount of reduced cytochrome c and a high level of cytochrome c oxidase activity.<ref name="Voet" /> An additional level of regulation is introduced by the transport rates of ATP and NADH between the mitochondrial matrix and the cytoplasm.<ref name="Brandolin" />