Urea Output by L(3) Teladorsagia circumcincta and some Properties of Two Urea Producing Enzymes

BACKGROUND: Like several other parasites, Teladorsagia circumcincta secretes or excretes urea, but neither 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 phenol/hypochlorite after treatment with urea aminohydrolase. The kinetics of creatine amidinohydrolase and arginine amidinohydrolase were characterised by coupling the reactions with urea aminohydrolase 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.