Nutrition Ch. 4

Trypsin

A protein-splitting enzyme secreted as the inactive proenzyme trypsinogen by the pancreas and that is activated and works in the small intestine to reduce proteins to shorter-chain polypeptides and dipeptides.

Chymotrypsin

A protein-splitting enzyme secreted as the inactive zymogen chymotrypsinogen by the pancreas; after it has been activated by trypsin, it acts in the small intestine to continue breaking down proteins into shorter-chain polypeptides and dipeptides.

Carboxypeptidase

A specific protein-splitting enzyme secreted as the inactive zymogen procarboxypeptidase by the pancreas; after it has been activated by trypsin, it acts in the small intestine to break off the acid (i.e., carboxyl) end of the peptide chain, thereby producing smaller-chained peptides and free amino acids.

Aminopeptidase

A specific protein-splitting enzyme secreted by glands in the walls of the small intestine that breaks off the nitrogen-containing amino end (i.e., NH2) of the peptide chain, thereby producing smaller-chained peptides and free amino acids.

Enterokinase

An enzyme produced and secreted in the duodenum in response to food entering the small intestine; it activates trypsinogen to its active form of trypsin.

Zymogen

An inactive enzyme precursor.

Proenzyme

An inactive precursor (i.e., a forerunner substance from which another substance is made) that is converted to the active enzyme by the action of an acid, another enzyme, or other means.

Dipeptidase

The final enzyme in the protein-splitting system that produces the last two free amino acids.

Dispensable amino acids

The five amino acids that the body can synthesize form other amino acids that are supplied through the diet an thus do not have to be consumed on a daily basis.

Pepsin

The main gastric enzyme specific for proteins; pepsin begins breaking large protein molecules into shorter chain polypeptides, and it is activated by gastric hydrochloric acid.

Rennin

The milk-curdling enzyme of the gastric juice of human infants and young animals (e.g., calves); rennin should not be confused with renin, which is an important enzyme produced by the kidneys that plays a vital role in the activation of angiotensin.

Indispensable amino acids

The nine amino acids that must be obtained from the diet because the body does not make adequate amounts to support body needs.

Conditionally indispensable amino acids

The six amino acids that are normally considered dispensable amino acids because the body can make them; however, under certain circumstances (e.g., illness), the body cannot make them in high enough quantities, and they become indispensable to the diet.