IDENTIFICATION OF HISTATINS AS TANNIN-BINDING PROTEINS IN HUMAN SALIVA

Tannins have a number of detrimental biological effects and these incl ude interference with normal growth and metabolism if they are present in the feed of various animals. Proline-rich proteins (PRPs) in saliv a have been shown to provide protection against tannin, but little is known about the mechanism of protection and interaction of other saliv ary proteins with tannin. To identify tannin-binding human salivary pr oteins, parotid and submandibular/sublingual saliva samples were adsor bed with tannin. PRPs, and in particular a group of low-M(r) proteins, were readily precipitated by tannin. The low-M(r) proteins were purif ied from parotid saliva and demonstrated to be histatins, a family of well-characterized histidine-rich salivary proteins. The ability of sy nthetic histatin 5, as well as an acidic PRP (PRP-1) and gelatin to pr ecipitate quebracho condensed tannin and tannic acid was determined. A t pH 7.4 histatin 5 was the most effective precipitant of both condens ed tannin and tannic acid and it also precipitated the largest amount of condensed tannin at pH 3.0, but the smallest amount of tannic acid at that pH. In contrast PRP-1 showed a greater ability to precipitate both condensed tannin and tannic acid at pH 3.0 than at pH 7.4. Under most circumstances histatin 5 was therefore more effective in precipit ating tannins than proteins with high proline content which generally have been recognized as strong precipitants of tannin. Preincubation o f tannic acid with alpha-amylase inhibited the enzyme, but addition of histatin 5 or the acidic PRP PIF-s protected amylase from inhibition by tannin. Similarly salivary proteins may protect other biological ac tivities in the digestive tract from inhibition by dietary tannin.