Characteristics of Sialidase in the Rat Salivary Glands

Abstract

Using 4-methylumbelliferyl-N-acetylneuraminic acid (4MU-NeuAc) as substrate, we measured sialidase activity in the salivary glands and other organs of the rat. The pH optima of salivary gland sialidase were between 4.0 and 4.5, which were similar to those of the enzyme in the brain, liver and kidney. Among the salivary glands, the submandibular one showed the highest sialidase activity followed by the parotid and the sublingual glands. However, sialidase activity in these glands was lower when compared with the activity in the brain, liver and kidney. From the subcellular distribution study, salivary gland sialidase was found to be mainly localized in the lysosomes. The pH optima of the lysosomal sialidase of the salivary glands were between 4.0 and 4.5; and K(m) values for 4MU-NeuAc approximately 0.09 mmol/1. In the submandibular and parotid glands, a soluble sialidase with a different pH optimum (5.5) and K(m) value (0.25 mmol/1) was also detected.

Sialidase in the Guinea Pig Pulmonary Parenchyma. Increased Activity in the Cytosolic and Microsomal Subcellular Fractions after Stimulation withBacillus Calmette Guérin

“…The apparent K m of the different forms of lung sialidase determined in this study, using the synthetic substrate Mu-NeuAc, are in agreement with those reported for sialidases extracted from different tissues [10,13,32] Storage of these enzymes at + 4 °C for 24 h resulted in a 10 to 30% loss of activity. It has been reported that sialidase activities were labile and that they could be stabilized by adding either exogenous protein such as bovine serum albumin^1 01 , or W-acetylneuraminic acid^3 21 .…”