Evidence for the presence of carbonic anhydrase 29-kDa isoenzyme in salivary secretions of three ruminating species and the gelada baboon

Salivary glands are highly variable in composition of their secretions and thus could be one of the primary ways by which species adapt or react to their environments. It has been hypothesized that feeding adaptation correlates with saliva composition. Hence, animals of different families using identical feeding niches should possess similar salivary proteins. For the first time, salivary secretions of grass-eating cattle, goat, camel and gelada baboon were compared by SDS-gel electrophoresis and immunoblotting. Salivary protein patterns were similar among individuals of the same species but varied largely among species. However, all samples showed proteins of apparently 29 and 42 kDa, identified as carbonic anhydrases (CA) by immunoblotting. The CA-VI (42 kDa) was highly expressed in cattle and camel saliva, but showed lower expression in goat saliva and could not be detected in gelada baboons. The CA-II (29 kDa) was found in saliva of all species tested and was shown in ruminating animals not to originate from cellular debris of the oral mucosa or ingested food. The results demonstrate that besides CA-VI, CA-II is another CA isoform secreted especially in ruminant saliva. Furthermore, the two CA isoenzymes detected may form a complementary system, protecting mucosa from acidity and helping to maintain a constant bicarbonate concentration in the animalʹs mouth and digestive tract.