Some of the amino acids that are liberated when proteins are degraded can be converted into intermediates of the Krebs cycle. When they enter the Krebs cycle the high energy electrons from these compounds can be transfered to NADH and/or FADH2 and subsuequently used to synthesize ATP via oxidative phosphorylation.
an example of this is shown in the figure below
Depending upon their struture, some amino acids can be deaminated and converted into intermediates of glycolysis. Once the intermediates enter the glycolytic pathway they can then enter the Krebs cycle and high energy electrons can be extracted to be used in oxidative phosphorylation.
Below are two examples of amino acids which when deaminated are converted to pyruvate.