Pharmacological and Biochemical Properties of Saxiphilin, a Soluble Saxitoxin-Binding Protein From the Bullfrog (Rana Catesbeiana)

Toxicon. 1991;29(1):53-71. doi: 10.1016/0041-0101(91)90039-t.


Supernatant fractions of various tissues and plasma from the North American bullfrog, Rana catesbeiana, specifically bind saxitoxin with high affinity. Binding of [3H]saxitoxin to bullfrog plasma follows single-site behavior with an equilibrium dissociation constant of Kd = 0.16 +/- 0.03 nM at 0 degrees C and a maximum binding capacity of 380 +/- 60 pmole/ml plasma. High-affinity binding of [3H]saxitoxin is chemically specific since it is unaffected by tetrodotoxin and a variety of cationic peptides, amino acids and drugs. The structure-activity dependence of binding to this site was investigated with eight different natural and synthetic derivatives of saxitoxin. Substitution of the carbamoyl side chain or the C-12 beta-hydroxyl group of saxitoxin with a hydrogen atom had little effect on binding affinity, but addition of a hydroxyl group at the N-1 position decreased the binding affinity from 430- to 710-fold in three different molecular pairs. High performance size exclusion chromatography of supernatant from bullfrog skeletal muscle showed that the [3H]saxitoxin-binding component migrates with an apparent molecular weight of Mr = 74,000 +/- 8000 or a Stokes radius of 35 +/- 2A. The [3H]saxitoxin-binding protein in skeletal muscle extract or plasma is retained on a cation-exchange column at pH 6.0, suggesting that the protein contains a region of exposed basic residues. Column isoelectric focusing of a sample from plasma indicated that the protein has a basic isoelectric point near pH = 10.7.(ABSTRACT TRUNCATED AT 250 WORDS)

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amphibian Proteins
  • Animals
  • Carrier Proteins / chemistry
  • Carrier Proteins / metabolism*
  • Chromatography, Gel
  • Chromatography, Ion Exchange
  • Isoelectric Focusing
  • Muscles / metabolism
  • Rana catesbeiana*
  • Saxitoxin / metabolism*
  • Sodium Channels / metabolism
  • Solubility
  • Structure-Activity Relationship


  • Amphibian Proteins
  • Carrier Proteins
  • Sodium Channels
  • saxitoxin-binding protein, Rana catesbeiana
  • Saxitoxin