How the sialylation level of serum N-acetyl-β-D-glucosaminidase a form in type 1 diabetes mellitus influences its activity?

It has been verified that serum N-acetyl-β-D-glucosaminidase (NAG) activity is elevated in diabetes, but there are no reports about changes of the sialic acid (SA) content in the carbohydrate parts of NAG A form and its influence on total NAG activity changes in type 1 diabetes mellitus patients without and with secondary complications. NAG A forms were isolated, purified and characterized from the serum of 81 IDDM patients with and without secondary complications (retinopathy, polyneuropathy and nephropathy) and 25 healthy persons. The content of α-2,6-bound SA and isoenzyme patterns of purified A form, total NAG and A form activities were determined. In all diabetic groups, A form sialylation levels were 2-3.5 times lower compared to control, while their acidities (fractions with pI 4.25-5.1) increased, particularly with progression of secondary complications. Total serum NAG activities and percentages of A form were significantly higher (P<0.001) in all diabetic groups and negatively correlated with the α-2,6-bound SA content of the A form. In addition, they decreased as secondary diabetic complications became more complex. Observed changes could be the consequence of structural changes in the A form due to significant increase in its acidity, i.e. negative charge which originate from groups other than SA. [Projekat Ministarstva nauke Republike Srbije, br. 172049