[Conformational states of pancreatic lipase]

Spin-label method was applied to the studies of conformation properties of pancreatic lipase. Spin-labelled derivatives of the enzyme in SH- and NH2-groups were obtained. ESR-spectra of both samples belong to the immobilized type, in the first case the ESR-spectrum corresponding to strong immobilization of the spin-label, and in the second--to the average one. In both cases the rotation correlation time of the enzyme molecule was measured. The time proved the same independent of the site of the label attachment; it corresponded to the rotation of macromolecule with molecular weight 50000. This fact points to the absence of both intramolecular flexibility of the enzyme molecule and of the association of lipase molecules in solution. It has been shown that introduction of substrates and inhibitors of the enzyme and the interface as well, induces no changes in the ESR spectra, which points to the absence of local conformation changes of protein near the spin-labels introduced.