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A procedure making use of the intracellular arginase activity has been developed for measuring the transport of arginine across the human erythrocyte membrane. (1) The arginine translocation is carrier mediated with simple Michaelis-Menten kinetics, showing one high affinity, low capacity transport system characterized by a half saturation constant KT of 0.177 +/- 0.036 mmol/1, and a maximum velocity VT of 0.332 +/- 0.068 mumol X h-1 X ml-1 cells. (2) Competition experiments with lysine, ornithine and leucine indicated that the arginine transport system in specific for dibasic amino acids. (3) The value calculated for the intracellular arginine concentration agreed well with the values obtained by independent methods. (4) The low arginine transport rate of human erythrocytes can explain the failure to lower the hyperargininemia in familial hyperargininemia by blood transfusion with normal arginase-containing erythrocytes.

By increasing diadenosine pentaphosphate to a final concentration of 75 mumol to 100 mumol/l to inhibit excess adenylate kinase, a highly sensitive substrate in a gelatin matrix allowed the developement of a simple and cheap electrophoretic technique for creatine kinase MM isozyme in dried blood samples. The method is suitable for neonatal Duchenne muscular dystrophy screening, and it is an alternative method for a previously described bio-luminescent assay, which requires special equipment.