Expert: Florence M Rollwagen - 9/30/2008

Question
Dear Florence,

Generally, what is the rate of degradation for an extracellular protein in the human body?  Specifically, what is the rate of degradation of the amino acids from the C-terminal end and from the N-terminal end?  Further, how long does it take for an extracellular protein (e.g., an ligand) to pass from the human body if it is not degraded.  Thank you.

Answer
Hi George:  Thanks for your question.  You are making some assumptions in your question which, I think, are not warranted.

Protein degradation rates will be dependent on the specific protein involved (eg, collagen, fibrinogen, etc) as well as the cells that are secreting the proteolytic enzymes.

For example, an extremely aggressive and metastatic cancer will secrete large quantities of matrix metalloproteases (MM) into the environment which will allow the cancer cells to migrate at a rapid rate.

Much slower proteolysis occurs in bone remodeling or muscle building.  

Proteins don't always degrade from one end or the other, sometimes clips are made in the middle.  Again, the rate will be dependent on the system you choose to study.

Third, what extracellular protein (NOT ligand) do you anticipate passing from the body?  Foreign proteins are always degraded.  The proteins in scar tissue remain for years.  I'm not sure what you mean by this question.

I hope this answer has helped you.  Please write back if you have more questions.

FM Rollwagen, PhD