ENZYMATIC DIAGNOSIS OF ASPARTYLGLYCOSAMINURIA BY FLUOROMETRIC ASSAY OF GLYCOSYLASPARAGINASE IN SERUM, PLASMA, OR LYMPHOCYTES

Serum, plasma, and lymphocytes from aspartylglycosaminuria (AGU) patie nts and carriers and from normal controls were incubated with a fluore scent glycosylasparaginase substrate, L-aspartic acid beta-(7-amido-4- methylcoumarin), and the release of 7-amino-4-methylcoumarin was measu red fluorometrically after incubation for 1-4 h. The mean glycosylaspa raginase (EC 3.5.1.26) activity in normal serum, plasma, and lymphocyt es was 20.2 (SD 5.0) mU/L (n = 24), 17.5 (SD 5.0) mU/L (n = 24), and 2 42 (SD 108) mU/g protein (n = 17), respectively. The corresponding val ues in the Finnish AGU patients were 0.7 (SD 0.4) mU/L (n = 10), 0.3 ( SD 0.3) mU/L (n = 10), and 6.0 (SD 4.6) mU/g protein (n = 7). No overl apping values were obtained between the AGU patients and the carriers in any of the samples, but the values between the carriers and control s were overlapping in 28 of 29 serum, 22 of 29 plasma, and 4 of 21 lym phocyte samples. Thus, the fluorometric glycosylasparaginase assay in various blood samples allows specific detection of the enzyme defect i n AGU, but cannot be used for reliable detection of carriers of the di sease.