The below mentioned article provides a note on fat respiration and protein respiration.
(i) Fat Respiration:
Fats are stored as triglycerides in cells, primarily of adipose tissue. They have a high energy content, and form a better fuel than the carbohydrates. They break up into fatty acids and glycerol in the cytoplasm before use in respiration.
Fatty Acids:
Fatty acids are broken by a series of reactions into 2-carbon acetyl coenzyme A. The latter enters the Krebs cycle.
Glycerol:
Glycerol combines with a phosphate group, forming phosphoglyceraldehyde. The latter enters glycolysis.
Energy Output:
A molecule of 18-carbon stearic acid on complete oxidation produces 147 high-energy phosphates. A 6-carbon glucose molecule yields 36 or 38 ATP. With this rate, an 18-carbon molecule is expected to give 3 times more energy (36 or 38 x 3 = 108 or 114 ATP) but it provides about 4 times more energy (36 or 38 x 4 = 144 or 152 ATP) than 6-carbon glucose produces.
(ii) Protein Respiration:
The proteins split into amino acids in the cytoplasm for use in respiration. The amino acids enter respiratory routes in two ways: deamination and transamination.
Deamination:
In deamination, an amino acid loses its amino group (- NH2) and changes into a keto acid. The latter may further change into pyruvic acid or acetyl coenzyme A. Pyruvic acid is oxidized to acetyl coezyme A. The latter enters the Krebs cycle.
Transamination:
In transamination, an amino group of an amino acid is transferred to an appropriate keto acid, forming a new amino acid and a new keto acid. The keto acids so formed are normal participants of glycolysis or Krebs cycle.