Fish Apolipoprotein‐A‐I Has Heparin Binding Activity: Implication for Nerve Regeneration

Abstract: This study provides evidence that apolipoprotein‐A‐I (apo‐A‐I), derived from fish plasma and nerve, has heparin binding activity. We have shown previously that injury in a regenerative CNS, such as that of fish optic nerves, leads to increased levels of apo‐A‐I in media conditioned by these nerves, as compared with media conditioned by noninjured nerves. In the present study, we have purified and characterized apo‐A‐I from both fish plasma and optic nerves. Sequence analysis of the 15 N‐terminal amino acids revealed that at least 14 amino acids are identical in these two purified apo‐A‐I samples. The purified apo‐A‐I derived from both fish plasma and optic nerves binds to heparin. Binding measurements using [³H]heparin followed by Scatchard analysis revealed that apo‐A‐I binds to heparin with relatively low affinity (K_D= 2.8 × 10⁻⁶M). Results are discussed with respect to the possibility that accumulation of apo‐A‐I in the extracellular matrix of fish optic nerves is made possible via heparin binding, like that to apolipoprotein‐E in mammals.