Enzymic glycation may decrease activity of erythrocytic delta-aminolevulinate dehydratase in diabetes mellitus
Ratnaike, S.; Blake, D.; Shevenan, P.
Clinical Chemistry 33(10): 1807-1810
1987
ISSN/ISBN: 0009-9147 PMID: 3665033 Document Number: 294666
The mean dithiothreitol (DTT)-activated activity of erythrocytic .delta.-aminolevulinate dehydratase (ALAD, EC 4.2.1.24, porphobilinogen synthase) in 20 nondiabetic subjects was 30.5 (SD 4.0) U per liter of erythrocytes; in 79 diabetics, this activity was 19.4 (SD 6.3) U/L, significantly less (P < 0.001). Further, we observed a significant (P < 0.01) negative correlation between activated ALAD activity and the concentration of glycated hemoglobin in the diabetics (r = -0.58). Hemolysate incubated in a 75 mmol/L solution of glucose in isotonic saline for 48 h at 37.degree. C lost more activated ALAD activity than did hemolysate incubated in 75 mmol/L glycerol in isotonic saline. Enzyme kinetic studies showed this loss of activity to be noncompetitive. Our data suggest that the loss of erythrocytic ALAD activity in diabetics, paralleling the increase in glycated hemoglobin concentrations, probably results from glycation of this enzyme.