secretory carbonic anhydrase ii – Finding the evolutionary key to the symbiosis of animal hosts and their cellulose - fermenting bacteria

introduction the parotid gland has the highest carbonic anhydrase (CA) activity of all ruminant salivary glands (1). Since the saliva is well buffered at a constant pH of 8 and flows continuously into the rumen, salivary CA might play an important role in maintaining a constant oral and ruminal milieu (2; 3). Especially, CA-II was shown to be essential for the production of regular amounts of saliva (4). In fact, almost half of the bicarbonate entering the rumen comes from saliva (5), where it is most likely produced by active carbonic anhydrases. One such enzyme is the secreted salivary CA-II, which is abundant in cattle and other ruminating animals such as camels or goats, whereas animals not necessarily relying on cellulosefermentation like baboons and humans have only small amounts of CA-II in their saliva (6).