Evidence for a Pancreatic Lipase Subfamily with New Kinetic Properties

Abstract

Several new members of the pancreatic lipase family have been reported recently, and amino acid sequence comparison reveals that this family can now be divided into three subgroups: (1) "classical" pancreatic lipases, (2) related proteins 1 (RP1), and (3) related proteins 2 (RP2) (Giller, T., et al. (1992) J. Biol. Chem. 267(23), 16509-16516). Whereas "classical" pancreatic lipases are well characterized with respect to kinetic properties, i.e., interfacial activation and dependence on colipase in the presence of bile salts, the two latter subfamilies have been poorly investigated so far. The kinetic behavior of a lipase from guinea pig pancreas differs, however, from that of "classical" lipases (Hjorth, A., et al. (1993) Biochemistry 32, 4702-4707). This enzyme is highly homologous to RP2 lipases with the exception of a deletion in the so-called lid domain that regulates access to the active center of pancreatic lipases. We have now characterized a novel lipase from coypu (Myocastor coypus) pancreas. This enzyme, also belonging to the RP2 subfamily, possesses a full-length lid domain, but its kinetic properties are very similar to those of the guinea pig enzyme: (1) a high phospholipase activity, (2) the absence of interfacial activation, and (3) the absence of a colipase effect at high bile salt concentrations. Since both guinea pig and coypu pancreas produce a classical pancreatic lipase and no measurable phospholipase A2 activity, it is suggested that RP2 enzymes act as real phospholipases under physiological conditions. In fact, all RP2 lipases from other species might share phospholipase activity and fulfill new biological functions.