Distribution of N-acetyl-beta-D-glucosaminidase isoenzymes along the rabbit nephron

Total N-acetyl-beta-D-glucosaminidase (NAG) activity has been measured in microdissected glomeruli (G) and tubular segments [proximal convoluted tubule (PCT), pars recta (PR), medullary thick ascending limb (MAL), and cortical collecting tubule (CCT)] of the rabbit kidney, by a fluorimetric method using synthetic substrate. Selective activity of the isoenzyme NAG B was also determined. Isoenzyme profiles of NAG were obtained by electrofocusing on each segment. Characterization of the isoenzymes was performed by chromatofocusing and thermosensitivity experiments on PCT. Total NAG activity, mainly composed of NAG A, was low in glomeruli and two and one-half to four times higher in PCT than in other segments, in which comparable activities were found. NAG B was detectable all along the nephron. It represented a very small fraction of total NAG, except in PCT where it was more abundant (20 to 30%). Electrofocusing revealed the presence of a minor form (NAG I) all along the nephron. Chromatofocusing and thermosensitivity studies indicated that NAG I could represent imperfectly solubilized NAG A rather than a well defined entity. From these results, it could be suggested that the reported increase in urinary excretion of NAG B after renal injury may reflect the intensity of proximal tubular lesions.