hydrolysis & modification of proteins

William Tivol tivol at news.wadsworth.org
Fri Sep 27 16:30:05 EST 1996


C Wood (bsscw at bath.ac.uk) wrote:

Dear Chris,

: Can someone help me out here .... i am going nuts trying to work out what
: some literature i am reading (which seems to contradict itself) says  ...
: 2 quick questions:

: 1) take some proteins ... say veg protein ... say soy protein and dissolve
: it in alkaline solutions and then add some NaOH and warm for 4 hours at
: 160F .... the protein is "hydrolysed" ... what does this mean exactly
: please ... 

	It means that the peptide bonds, which link the amino acid resi-
dues into the protein chain, have been broken.  An H is linked to the NH
at one end of the residue (forming NH2--amino) and an OH is linked to the
CO at the other end (forming COOH--acid), and H + OH = water; thus "hydro-
lysed", meaning split (lysed) by water.  A generic amino acid can be writ-
ten:

		NH2-CHR-COOH

where R is a different group for each amino acid; a protein looks like:

		NH2-CHR1-CONH-CHR2_CONH-...-Rn-COOH.
                           
At pH different from 7, either the COOH loses H+ to become COO- or the
NH2 gains H+ to become NH3+, depending on whether the solution is basic
or acid.

: 2) what will happen to, for example, amine functional groups on some
: dissolved soy protein (which has not been "substantially hydroysed" but
: has been reduced meaning any/all disulfide bonds are broken) .. what
: differences will u expect to see if this acetylation/modification is
: performed at acid pH or alkaline pH?   please help me 

	Since NH2 is already reduced, nothing should happen to it if the
protein is subjected to the usual reducing conditions (this is not to say
that there are not conditions where further reduction is possible).  If
the reduction is carried out at non-neutral pH, this should not change;
however, hydrolysis can occur due to the pH independently of the reduction.
				Yours,
				Bill Tivol



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