The activity of selected soluble enzymes in the avian nasal salt gland

Abstract

AbstractTen adult western gulls (Larus occidentalis) ranging in weight from 761–1,004 gm were studied. The gulls were fed 3% NaCl in their drinking water. They were killed by decapitation, and the salt glands, weighing 0.51–0.78 gm were cooled, homogenized in 0.14 M KCl, centrifuged at 0–4°C at 20,000 × G for 30 minutes and the supernatant used for all enzymes assays. All assays were conducted at 25°C by observing the changes in absorbancy with time using a Gilford Multiple Absorbance Recorder. The enzymes were assayed by measuring either the appearance or disappearance of NADH or NADPH at 340 mμ. The average units of enzyme activity (the amount of enzyme required to form 1 μM of substrate per minute ) per gram of salt gland were as follows: phosphoglucomutase, 0.62; glucose‐6‐phosphate dehydrogenase, 1.40; aldolase, 2.86; lactic dehydrogenase, 90.1; isocitric dehydrogenase, 5.08; malic enzyme, 0.92; glutamic‐oxaloacetic transaminase, 100.5; and glutamic‐pyruvic transaminase, 0.50. The protein content of the salt glands varied from 62.5–87.6 mg protein/gm. On the basis of an adjusted calculation of energy yields from the glycolytic scheme and the Krebs cycle, it would appear that only one‐third of the energy derived from these pathways would be necessary to maintain the maximum rate of salt secretion, leaving the other two‐thirds for other cellular processes. Glutamate metabolism may also be important as an energy source in the salt gland.