Subject: Re: Nutrition; Types of Protein
From: Jay_Mann@equinox.gen.nz (Jay Mann)
Date: Jun 28 1995
Newsgroups: misc.fitness.aerobic

j.g. duplantie (jduplant@julian.uwo.ca) wrote:
: 
:    i read in 'fit for life' by harvey diamond that eating foods that 
: contained amino acids was better than eating foods that contained protein 
: because your body has to break down animal protein into amino acids 
: anyway.  


Warning, warning!  Snake oil alarm activated!
What is supposed to be so bad about having to break down food proteins?  The
body is rather well adapted to this kind of activity, and I really wonder if
there would be long-term health consequences of _not_ eating proteins.  

There are three "endopeptidase" enzymes that start off the job: pepsin in
the (acid) stomach; trypsin and chymotrypsin in the (alkaline) intestine. 
Pepsin mainly attacks bonds with aromatic side-chains (tyrosine &
phenylalanine) although it also hits glutamic, cysteine and cystine groups. 
Trypsin attacks bonds where the carboxyl group comes from basic amino acids
arginine or lysine.  Chymotrypsin works best against aromatic amino acid
links (tyrosine, phyenylalanine and tryptophan) with slower action against
leucine, methionine, asparagine, and glutamic acid groups.  Thus
chymotrypsin action overlaps pepsin, in case something went amiss during the
stomach period of digestion.  (For instance, the food might not have been
chewed up enough to let the stomach juices penetrate fully.)  There is a
third enzyme, elastase, which acts mainly on alanine bonds.

The above endopeptidases have chopped internal bonds in the protein
structure.  Now the smaller pieces are chewed to bits, starting at one end
and working inwards, that is, by exopeptidases, primarily carboxypeptidases
A and B.  The A enzyme is optimized to attack the results of chymotrypsin,
whereas the B enzyme is optimized to attack the results of trypsin action. 
The results are small molecules having about six amino acid groups in a
chain.

The final steps involve cutting these small hexa-(6)-peptides  into amino
acids using enzymes that are physically localized in the surface layers of
the inside of the small intestine.

The production and release of trypsin, etc is controlled by internal systems
that stimulate the activity of the pancreas gland. The release of partially
macerated food from the stomach into the small intestine (duodenum being the
name for the first section) stimulates release of pancreatic juice by means
of a hormone called secretein. Pancreatic juice contains both starch- and
protein-digesting enzymes, but there may be partially independent control of
both types of enzyme.  For instance, as dietary starch goes up, the
pancreatic juice eventually contains more alpha-amuylase than before; the
control mechanism may be through nerves rather than hormones.  Other hormone
control mechanisms stimulate production or release of fat-digesting and
protein-digesting enzymes.

Finally, there is negative feedback: when there are excess amounts of
trypsin in the small intestine, further production of trypsin is
diminished.

And you are proposing to muck around with this beautiful regulatory system,
feeding it pre-hydrolysed proteins, just because some author tells you to do
so?  

Jay D Mann  <jmann@equinox.gen.nz>
Christchurch, New Zealand


 They cleave a relatively small number of bonds, that is, they cut proteins
down into rather big chunks.  Then there are additional intestinal enzymes