Cloning, Partial Sequencing and Expression of Rabbit Lacrimal Gland β-Hexosaminidase

Abstract

Several proteins actively secreted by the lacrimal gland have now been identified, including lactoferrin, lysozyme, tear specific pre-albumin and secretory IgA in human tear fluid.¹ In addition, some lysosomal hydrolases have also been detected in tears and lacrimal gland fluid.^2,3 In our ongoing studies of rabbit lacrimal gland acinar cells in primary culture, we noted that β-hexosaminidase catalytic activity, which we had expected to serve as a marker for lysosomes, diverged from another potential lysosomal marker, cathepsin B. Both enzymes were distributed primarily to the soluble phase, consistent with release from disrupted vesicular and cisternal structures. However, the membrane-associated component of hexosaminidase activity, when compared to cathepsin B, showed a relatively greater steady-state content in membranes of the endoplasmic reticulum and Golgi complex, suggestive of a product undergoing significant bulk flow through the synthesis and assembly pathway.^4,5 Since β-hexosaminidase has been reported to be present in human tears,^6,7 we examined the possibility that β-hexosaminidase might serve as a marker of regulated protein secretion by rabbit lacrimal gland acinar cells (Gierow et al., submitted).^8,9