Kinetical Properties of the Serum Mannan-Binding Protein from Rabbit.¹ A Comparison with Those of the Liver Mannan-Binding Protein

Abstract

A serum lectin specific for mannose and N-acetylglucosamine residues (serum mannan-binding protein) was characterized as a glycine-rich protein of large molecular size. Binding of the lectin to ¹²⁵I-labeled mannan was a reversible and saturable process with a dissociation constant of 2.3×10^-9 M and a maximum capacity of 3.6 pmol of ¹²⁵I-labeled mannan per pg of protein. α-Mannosidase, a lysosomal enzyme isolated from porcine kidney, bound to the lectin with high affinity (K_d=2.8×10^-9 M). These kinetical parameters are compared with those of the liver mannan-binding protein in a discussion of the interrelationship of these two lectins.