How are the products of protein hydrolysis by an aminopeptidase used in metabolism?

Aminopeptidases are enzymes that cleave polypeptides, or proteins,at the N terminus, or the amino end.  Protein hydrolysis is breaking down proteins into amino acids by adding water. Aminopeptidases are enzymes that cause protein hydrolysis. Once the protein is broken down into amino acids, the amino acids can be metabolized. Usually the body uses carbohydrates or lipids for metabolism, but in rare cases, such as starvation, proteins can be broken down and used for energy. 
Protein metabolism starts with the enzyme,pepsin, in the stomach and the smaller polypeptides travel to the small intestine where trypsin and chymotrypsin break them down into amino acids. Most of the newly available amino acids are combined to form new proteins. If the body has no need for proteins, they are converted to glucose or ketones and are decomposed. Breaking down amino acids results in nitrogen, which is converted to urine. In starvation, protein is broken down to amino acids and amino acids are broken down to oxaloacetate  acid, pyruvate  and acetyl coA and these intermediates are used in the Kreb cycle to produce ATP. 

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