Role of a sulfhydryl group in gastric lipases

Abstract

Native human and rabbit gastric lipases (HGL and RGL, respectively) were inactivated after modification of one sulfhydryl group/enzyme molecule. HGL and RGL were covalently labeled using 5,5′‐dithiobis(2‐nitro‐[¹⁴C]benzoic acid) and the interaction of 2‐nitro‐5‐thio‐[¹⁴C]benzoic‐acid‐labeled lipases ([¹⁴CINbs‐lipases) with monomolecular lipid films was investigated. Our results show that [¹⁴C]Nbs‐lipases bind to lipid films as efficiently as native HGL or RGL. The critical surface pressure π_c and the maximal surface pressure (Δπ^max) of [¹⁴C]Nbs‐lipases were enhanced in comparison with those of native RGL and HGL. These change in behavior were probably due to an increase in hydrophobicity brought about, directly or indirectly, by the binding of the Nbs radical. This chemical modification thus blocks the hydrolysis site and reinforces the hydrophobic character of the gastric lipases