tivol at tethys.ph.albany.edu tivol at tethys.ph.albany.edu
Wed Nov 30 11:30:10 EST 1994

	Histidine is, indeed, an amino acid:

		|   |
		N   NH
And histamine is a metabolic product which causes several reactions involving
the immune system.  It is associated not only with alergies, but is also part
of the immune response to infections, etc.  It causes dilation of the capil-
laries, which allows lymphocytes to infiltrate tissues more readily, and has
several other effects.  Its structure is

		|   |
		N   NH
Either can pick up a proton to become charged:

		|   |
	       HN + NH
where R is COOH for histidine and H for histamine.
	As you said, histidine is essential in infants.  A good biochemistry
text should give you more information.  Good luck.
				Bill Tivol

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