Kinetical properties of the serum mannan-binding protein from rabbit. A comparison with those of the liver mannan-binding protein.

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 X 10(-9) M and a maximum capacity of 3.6 pmol of 125I-labeled mannan per microgram of protein. alpha-Mannosidase, a lysosomal enzyme isolated from porcine kidney, bound to the lectin with high affinity (Kd = 2.8 X 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.