When is a protein not a peptide??

[Jonathan Ewbank]

bob.gross at dartmouth.edu (Bob Gross) writes:

>A peptide is ALWAYS a protein. 

well, to muddy such clarity of vision:

if a protein is truncated by a protease often it releases a peptide, not a 
protein. 


>Peptides are single chains of amino acids. A
>protein can consist of one or more peptides. So for proteins that have a single
>"subunit" (a bit of an oxymoron!) the protein and the peptide are the same
>thing. For proteins that consist of many subunits (e.g. hemoglobin), the
>peptides are only part of the whole protein.


an alternative definition: "a short chain of residues with a defined 
sequence. there is no maximum number of residues in a peptide, but the 
term is appropriate to a chain if its physical properties are those 
expected from the sum of its amino acid residues and if there is no fixed 
three-dimensional conformation."

from "proteins, structures and molecular properties" by t.e. creighton 
(my old supervisor)


regards

j


ewbank at monod.biol.mcgill.ca