urea output by l3 teladorsagia circumcincta and some properties of two urea producing enzymes.

background: like several other parasites, teladorsagia circumcincta secretes or excretes urea, but nei-ther the rate of efflux nor the possible metabolic sources of the urea has been considered. methods: parasites were maintained by passage through sheep. urea efflux was measured using phe-nol/hypochlorite after treatment with urea aminohydrolase. the kinetics of creatine amidinohy-drolase and arginine amidinohydrolase were characterised by coupling the reactions with urea ami-nohydrolase and glutamate dehydrogenase. results: infective l 3 t. circumcincta secreted or excreted urea at 25% of the rate of nh 3 /nh 4+ . the rate of urea efflux was about 84 pmol h -1 (10 3 larvae) -1 over 4 hours, corresponding to about 11 nmol h -1 mg -1 protein. we could not detect urea aminohydrolase activity, but urea production by both creatine amidinohydrolase and arginine amidinohydrolase could be detected. the apparent k m and v max of creatine amidinohydrolase were 1.1 mm and 48 nmol h -1 mg -1 protein, respectively, and the activity was greatest at ph 8. the apparent k m and v max of arginine amidinohydrolase were 0.7 mm and 62 nmol h -1 mg -1 protein, respectively, and the activity was greatest at ph 7.9. conclusion: the activity of creatine amidinohydrolase and arginine amidinohydrolase was sufficient to account for the rate of urea secretion or excretion.