Keyhole limpet hemocyanin type 2 (KLH2): Detection and immunolocalization of a labile functional unit h

Keyhole limpet hemocyanin (KLH) is a mixture of two hemocyanin isoforms, te rmed KLH1 and KLH2. Within KLH1 eight oxygen-binding functional units (FUs) , 1-a to 1-h, have been identified, in contrast to KLH2, which was previous ly thought to be organized in seven FUs (2-a to 2-g). By limited proteolysi s of KLH2 subunits, isolation of the polypeptide fragments, and N-terminal sequencing, we have now identified an eighth FU of type h, with a molecular mass of 43 kDa. This is unusually small for a FU h from a gastropodan hemo cyanin. It is also shown that KLH2 didecamers can be split into a stable an d homogeneous population of decamers by dialysis against 50 mM Tris/HCl, pH 7.5, in the absence of divalent cations. Electron microscopic immunolocali zation using a specific monoclonal antibody reveals that FU KLH2-h is locat ed at the collar of the decamer. (C) 1999 Academic Press.