Purification and use of limulin: A sialic acid-specific lectin

A simple and rapid method for the isolation of the sialic acid-specific lectin, Limulus polyphemus hemagglutinin (LPA), from the hemolymph of Limulus polyphemus is described. Declotted hemolymph is adsorbed to an affinity chromatographic column consisting of hog gastric mucin glycopeptides coupled to agarose and LPA is eluted in a single step with a Ca²⁺-free buffer, giving an apparent purification of ~25,000-fold. The eluted material is homogeneous by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and isoelectric focusing and consists of identical subunits each of 29,000 daltons. Hemagglutination inhibition studies with horse red blood cells indicate specificity of LPA for N-acetyl-and N-glycolylneuraminic acid; binding is Ca²⁺-dependent and abolished by neuraminidase treatment. LPA was covalently coupled to rhodamine and to horseradish peroxidase for use in detection of sialoglycoconjugates on cells and tissues by light and electron microscopy. Examples of the use of LPA for detection of sialoglycoconjugates in rat renal tubules and glomeruli, blood vessels in rat pancreas, and on horse red blood cells are shown. The procedures described here should prove useful as a cytochemical probe for detection of sialoglycoconjugates in a variety of systems. An accompanying article utilizes these probes for the detection of sialoglycoconjugates on the plasmalemma of adult and differentiating rat pancreatic acinar cells.