HUMAN COLON SIALIDASE - CHARACTERIZATION AND ACTIVITY LEVELS IN NORMAL MUCOSA AND COLONIC ADENOCARCINOMA

Human colon sialidase has been characterized, and its activity levels in normal mucosa and colonic adenocarcinoma have been determined. Sial idase activity was maximal at pH 5.5, and was unstable with storage at 4 and -20 degrees C. The bulk of activity was pellet-associated, and could not be released with triton X-100 or lamidopropyl]-dimethylammon io)-1-propanesulfonate. Using '-(4-methylumbelliferyl)alpha-D-N-acetyl neuraminic acid as substrate, the K-m and V-max values were estimated to be 0.140 mmol/l and 63 mU/g, respectively. Furthermore, an inhibiti on by substrate concentrations above 1.5 mmol/l was detected. Neuramin ic acid caused a competitive inhibition with a K-i of 3.5 mmol/l. A st atistically significant increase (p < 0.001) in the sialidase specific activity was found in primary colonic adenocarcinoma (103.20 +/- 8.00 mU/g) compared to that of the normal mucosa (72.50 +/- 7.67 mU/g).