Human salivary arginase and its deficiency in argininaemia

Arginase from normal human mixed saliva was characterized. The enzyme was completely activated after a preincubation of 20 min at 55 degrees C and a Mn2+ final concentration of 5 mmol/l. The pH optimum was 9.6-9.8, and the Km for L-arginine was 4.2 +/- 0.7 mmol/l. In normal saliva only one form was found, which was chromatographically identical with the cationic form of arginase in liver and blood cells. Salivary arginase was completely precipitated by rabbit antiserum against human liver arginase. Arginase activity was not detectable in the saliva of patients suffering from argininaemia. Enzyme activities in the saliva of the heterozygous parents and the unaffected daughter were 0.08, 0.07 and 0.12 U/mg protein, respectively, whereas the activities in the saliva of 60 healthy adults and 8 children were 0.17 +/- 0.11 and 0.16 +/- 0.06 U/mg protein, respectively.