[Multiple molecular forms of human plasma butyrylcholinesterase. I. Apparent molecular parameters and broad pattern...

Apparent molecular parameters (molecular weights, sedimentation constants, partial specific volumes, free electrophoretic mobilities and isoelectric points) of the four molecular forms C-1, C-2, C-3 and C-4 of human plasma butyrylcholinesterase (EC 3.1.1.8) have been demonstrated by polyacrylamide gel electrophoresis methods and centrifugation in sucrose gradient. The C-1 component is the monomeric form of the enzyme )Mr = 84 800 +/- 5800). All the forms are partially interconvertible and C-1, C-3, C-4 are size isomers corresponding to the monomer, dimer and tetramer of the enzyme. An estimation of the general shape of these forms attempted from electrophoretic and hydrodynamic parameters suggests that they are prolate ellipsoids. The C-4 component in which the axial ratio is at least equal to 8 appears to be arranged as a dimer of dimers (C-3)2 in which the two units are associated in a quasi-linear fashion. The C-2 component is composed of C-1 associated with an inactive smaller subunit, which is responsible for its specific electrical properties (mobility and isoelectric point).