Increased manganese content and reduced arginase activity in erythrocytes of a patient with prolidase deficiency (iminodipeptiduria).

Manganese was measured in blood of a patient with prolidase deficiency by neutron activation analysis. The manganese content of packed blood cells was 48.9 ng/g wet weight (controls 18.4 +/- 4.3 ng/g wet weight). It was proportionately increased in whole blood, whereas the serum manganese concentration was unchanged. The erythrocyte arginase activity was reduced to 46% of the mean control value. The reduced activities of two manganese-dependent enzymes, prolidase and arginase in erythrocytes in combination with an increased manganese content cannot be explained at the moment and leads to the speculation that manganese is inaccessible for enzyme activation.