Is the unique negatively charged polypeptide of crayfish yolk HDL a component of crustacean vitellin?

The yolk protein of Cherax quadricarinatus contains six major high-density lipoprotein (HDL) subunits with the approximate molecular masses of 177, 15 5, 106, 95, 86, and 75 kDa, of which only the 106-kDa polypeptide is negati vely charged. On the basis of their molecular weights, time of appearance a nd disappearance, their floating density and susceptibility to enzyme degra dation (by a serine proteinase), these six HDL polypeptides were classified into two subgroups. One group comprises the higher-molecular-weight compou nds above 106 kDa, and the other includes the lower-molecular-weight compou nds up to 95 kDa. Other than being different from the lower-molecular-weigh t polypeptides, the negatively charged 106-kDa polypeptide was significantl y different from members of its higher-molecular-weight group belonging to a different, less abundant, yolk protein as shown by HPLC separation. Immun ological studies and peptide mapping in which the 106-kDa polypeptide did n ot show similarity to any of the other HDL components confirmed these diffe rences. Moreover, the amino acid composition of the 106-kDa polypeptide was different from that of known vitellin from other crustacean species. This unique negatively charged polypeptide presents an enigma as it is known to be a secondary vitellogenic-related HDL polypeptide, immunolocalized in yol k globules; however, it is different to all the other HDL polypeptides, thu s presenting the question whether it is indeed a component of "classical" c rustacean vitellin. (C) 2001 Wiley-Liss, Inc.