P.J. Austin’s research while affiliated with Miami University and other places

Ansrnacr.-Mule deer (Odocoileus hemionus), domestic sheep (Oois aries), and American black bears (Ursus americanus) were fed quebracho (Schinopsis sp.) tannin to determine the contribution of salivary proteins to nitrogen- and fiber-digestive efficiencies and tannin metabolism. These values were compared to previously published values for laboratory rats (Ratfus rattus) and prairie voles (Microtus ochrogaster). Mule deer, black bears, and laboratory rats consumrrrg this condensed tannin produced tannin-binding salivary proteins that reduced fecal-nitrogen losses per unit of ingested tannin and reduced tannin metabolism relative to domestic sheep and prairie voles. Digestibility of the plant fiber was reduced significantly by tannins in domestic sheep, but not in mule deer. Although virtually all ingested tannin (98.3 + 5.0%) was recovered in feces of mule deer and black bears, ca. 25% was not recovered in feces of domestic sheep and presumably was metabolized. The defensive role of tannins as digestion inhibitors or toxins is dependent upon the molecular characteristics of the tannin interacting with the physiological capability of the animal. Results from one plant-mammal interaction cannot be used to interpret others without an understanding of the characteristics of the tannins and the physiology, ecology, and evolution of the animal.

A method has been developed for detecting tannin-binding proteins in the saliva of herbivores. The method is simple and requires only small quantities of crude saliva. The saliva of deer, a browsing ruminant, has been compared to that of domestic sheep and cow, which are grazing ruminants. The browser, which normally ingests dietary tannin, produces tannin-binding proteins, while the grazers do not produce such proteins. The tannin-binding protein from deer saliva is a small glycoprotein containing large amounts of proline, glycine, and glutamate/glutamine. The protein is not closely related to the proline-rich salivary proteins found in rats and other nonruminant mammals.

A simple continuous assay for plant pectin methyl esterase (EC 3.1.1.11) has been developed. During the enzymatic reaction, the galacturonic acid methyl esters in pectin are hydrolyzed, producing acid. In the assay, the pH indicator bromothymol blue is protonated to produce a change in the absorbance at 620 nm. The absorbance change is spectrophotometrically monitored. The assay is calibrated with galacturonic acid. The sensitivity of the assay is 0.020 μmol of acid produced/min, and the precision is 12% (relative standard deviation). The assay requires only 2-3 min and 2 mL of substrate/trial. The measured activities are directly proportional to the amount of commercial pectin methyl esterase added, and the activity obeys saturation kinetics. In addition, the assay can be used to determine pectin methyl esterase in crude extracts of plant tissues. There is no interference from colored components or other activities in the extracts.