A Protein in Normal Nurse Shark Serum which Reacts Specifically with Fructosans

Abstract

The purified fructosan-specific protein (FSP) from normal nurse shark serum showed several bands in acrylamide gel electrophoresis, pH 9.3. Three purified preparations from three individual sharks appeared to have the same banding pattern but two pools from four shark sera showed a different band distribution. One preparation of FSP appeared as a single symmetrical peak on analytical ultracentrifugation with an s⁰_20,w of 10.64; the other showed two bands. The molecular weight calculated from sedimentation velocity, viscosity measurement and partial specific volume is 280,500. The protein contains four subunits linked noncovalently. Amino acid analysis showed large amounts of aspartic acid, glutamic acid, serine, threonine and cystine. No carbohydrate was detected. The circular dichroism spectrum of the purified FSP showed a negative peak at 220 to 222.5 nm. In the near ultraviolet, three positive bands were seen at 289, 280 and 268 nm. When sugars which bind specifically to FSP were added to the protein solution, increased ellipticities were seen between 260 to 285 nm with no change below 240 nm.