ONE-STEP IMMUNOAFFINITY PURIFICATION AND PARTIAL CHARACTERIZATION OF HYPOPHYSEAL GROWTH-HORMONE FROM THE AFRICAN CATFISH, CLARIAS-GARIEPINUS (BURCHELL)

Growth hormone (GH) was purified from African catfish (Clarias gariepi nus) pituitary extracts in a single step by use of immunoaffinity chro matography. A monoclonal antibody to chicken GH, which labels the catf ish hypophyseal somatotropes in immunocytochemistry, was coupled to CN Br-activated Sepharose, and crude alkaline pituitary extracts were run over the immunoadsorbent. Reversed-phase high-performance liquid chro matography analysis of the eluted material suggested heterogeneity, wh ereas silver staining upon SDS-polyacrylamide gel electrophoresis show ed one single band with an estimated molecular weight between 22,000 a nd 23,000 Da. Matrix-assisted laser desorption ionization time-of-flig ht mass spectrometry analysis of the same preparation revealed the pre sence of several components with molecular weights ranging from 20,170 to 20,900 Da. The amino terminus of the protein was homogeneous, and the first 50 residues matched the proposed sequence of GH from two oth er siluran species (Ictalunus punctatus and Pangasius pangasius), exce pt for one substitution at position 3. These data unequivocally confir m the identity of the purified molecule as suggested by immunochemical evidence. The bioactivity of the GH preparation was demonstrated by t he short-term effect of GH on T-3 plasma levels in juvenile catfish.