Exogenous and endogenous protein metabolism

 Exogenous and endogenous protein metabolism

Definition

Endogenous protein metabolism is the disintegration of those proteins which already exist as components of living cells (tissue proteins).

Exogenous protein metabolism is the breakdown of food proteins which do not exist as parts of the cell protoplasm.

The body proteins are continually broken down and replaced by new proteins synthesized from dietary amino acids. The replacement of protein is rapid in plasma, liver, kidneys and intestinal tract and slow in haemoglobin, muscle and skin.

Dynamic state of amino nitrogen and proteins of the body

It has been established by the work of Schoenheimer and others that the amino nitrogen of amino acids (except lysine) is distributed to other amino acids of different tissues and reversibly it is withdrawn from those amino acids to the amino acids which contained amino nitrogen by the process of deamination and reamination.