AN ENZYMATICALLY ACTIVE TRUNCATED FORM (-55 N-TERMINAL RESIDUES) OF RABBIT GASTRIC LIPASE - CORRELATION BETWEEN THE ENZYMATIC-ACTIVITY AND DISULFIDE BOND OXIDOREDUCTION STATE

Rabbit gastric lipase (RGL) was subjected to proteolysis with trypsin and led to cleavage occurring at three defined sites (Lys-4, Arg-55 an d Arg-229). The tryptic hydrolysate contained four fragments: Gly-230- Lys-379 (T1), Gly-56-Arg-229 (T2), Ser-5-Arg-55 (T3), as well as a 45 kDa molecular form consisting of peptides T1 and T2 linked by a disulf ide bridge. The tryptic hydrolysate of RGL as well as the 55 N-termina l amino acid deleted forms conserved 30% of the initial enzymatic acti vity in a tributyrin assay. Two out of the three cysteine residues whi ch are present in all the known gastric lipases were found to be invol ved in a disulfide bridge. Unlike HGL, RGL appears to have a heterogen ous pattern of cysteine residues. The 30% enzymatic activity of RGL pe rsisting after trypsin treatment may be attributable to the 45 kDa mol ecular form (with the Cys-227-Cys-236 or Cys-227-Cys-244 disulfide bri dge). Trypsin-treated HGL, which was completely inactivated, showed th at a single location of the disulfide bridge existed between cysteine residues 236 and 244. It can be concluded that the existence of one di sulfide bridge is necessary to maintain the lipase activity of the 45 kDa form of RGL. (C) 1998 Elsevier Science B.V. All rights reserved.