Source of ammonia excreted by the gills of the marine teleost, Myoxocephalus scorpius

Abstract

Measurement of ammonia concentration differences in blood entering and leaving gills showed that only about 12% of branchially excreted ammonia could be accounted for by the disappearance of blood ammonia. Gill tissue homogenates contained significant glutaminase I and glutamic acid dehydrogenase activities. The combined activity of both enzymes was more than sufficient to account for the branchially excreted ammonia. Furthermore, there was a significant deamination of blood glutamine by gill tissue. Thus, it is likely that the ammonotelism of teleosts is due to the enzymatic deamination of glutamine and other amino acids in the gill.