now enzymes

July 21, 2003

Emmanuel

I have a question for you on digestive enzymes. Why would protease, amylase and lipase from a vegetable source be active at low pH, while from pancreas destroyed by the acidity?

Alon

Hi Alon,

I really don't know much about plant enzymes. I'm mostly a one species scientist. But if what you say is true, that the plant enzymes are only active in acid pH's, then that must the chemical environment into which the plant secretes them. Enzymes are specific to the tissues and organs which they serve ... at least in humans. If a plant enzyme works in an acidic environment, then it may function in the human stomach if it can function at very low pH's of 2 or so. It would not function in the human small intestine with pH's of 8 to 8.4.

I don't think pancreatic enzymes are exactly "destroyed" by low pH. I think they are denatured. That is, they change shape in the acidic pH to the wrong shape for their activity. They may become active if bicarbonate secretion is sufficient to change the acid pH to 8 or 8.4. Acidic chyme from the stomach needs to be acted upon by bicarbonate secreted by the pancreatic duct cells and the bile duct cells. Once the bicarbonate secretion is sufficient to raise the pH to 8, then the pancreatic enzymes will work. But then the plant enzymes that need an acid pH will not work.

Emmanuel Segmen

July 21, 2003

But if what you say is true, that the plant enzymes are only active in acid pH's, then that must the chemical environment into which the plant secretes them.

>>>But since they are both the same protein (protease, amylase and lipase )an acid pH should denature them as well? What am I missing?

Alon

July 22, 2003

Alon,

Good question if I understand correctly. A protein is over 1,000 amino acids long. Each amino acid side chain may have a negative charge, a positive charge or may be non-polar. So the 1,000 unit thread will fold differently in different environments. In an acid environment, positively hydrogen ions will cover up the negative charges and may add extra positive charges. In a basic environment those negative charges will be exposed and predominate and will cause different folding. The stomach secretes pepsin (a protein enzyme peptidase) that becomes activated by hydrochloric acid and only works in the stomach's acid environment. The pancreas secretes trypsin (a protein enzyme peptidase) which gets activated in the small intestine and only works in basic pH's of around 8 to 8.4. They are both protein enzyme peptidases. They are both a long chain polypeptide. One of them folds correctly in an acid environment. The other one folds correctly in a basic environment. Thus, enzymes can be made for a wide variety of environments and are specific for the environment as well as for the substrate (or molecule) it acts upon.

It's possible I still haven't answered your question. Your question may be: If enyzmes are proteins, why don't enzymes metabolize enzymes? Sometimes they do, but generally they don't because enzymes do not offer up their peptide bonds for metabolism the way a structural protein would.

Emmanuel Segmen

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Alon Marcus

Monday, July 21, 2003 8:45 PM

Re: now enzymes

But if what you say is true, that the plant enzymes are only active in acid pH's, then that must the chemical environment into which the plant secretes them.

>>>But since they are both the same protein (protease, amylase and lipase )an acid pH should denature them as well? What am I missing?

Alon