5-Bromo-indol-3-yl 5-acetamido-3,5-dideoxy-α-d-glycero-d-galactononulopyranosidonic acid, a novel chromogenic substrate for the staining of sialidase activity

Abstract

The purification and characterisation of viral, bacterial and mammalian sialidases (EC 3.2.1.18, neuraminidases, neuraminosylglycohydrolases) prompted a search for a colorimetric technique to localize the enzymes on electropherograms. The 5-bromo substituted indol-3-yl α-ketoside of 5-N-acetyl-d-neuraminic acid (BIN), the synthesis of which is described here, seemed to be the appropriate substrate, because of its relative ease of enzymatic hydrolysis to 5-N-acetyl-d-neuraminic acid and 5-bromoindoxyl. The latter is readily transformed to the insoluble, intensely coloured 5,5′-dibromo-indigo. This precipitates and can be seen readily at the sites of enzymatic activity. The new substrate is of definitive advantage as it provides a simple and direct method for the demonstration of sialidases without the need of a coupling reaction.