Subunit composition of the zinc proteins alpha- and beta-lipovitellin fromchicken

Chicken alpha- and beta -lipovitellin are derived from parent vitellogenin proteins and contain four subunits (125, 80, 40, and 30 kDa) and two subuni ts (125 and 30 kDa), respectively. Metal analyses demonstrate both are zinc proteins containing 2.1 +/- 0.2 mol of zinc/275 kDa per alpha -lipovitelli n and 1.4, +/- 0.2 mol of zinc/155 kDa per beta -lipovitellin, respectively . The subunits of beta -lipovitellin, Lv 1 (MW 125 kDa) and Lv 2 (MW 30 kDa ), are separated by gel exclusion chromatography in the presence of zwitter gent 3-16. Zinc elutes with Lv 1, suggesting that this subunit binds zinc i n the absence of Lv 2. The subunits of alpha- and beta -lipovitellin were s eparated by SDS-PAGE, digested with trypsin, and mapped by reverse-phase HP LC. The peptide maps of the 125-kDa subunits from alpha- and beta -lipovite llin are essentially identical. Similar results are obtained for the 30-kDa subunits of both lipovitellins, The sequences of five and four peptides of the 125-kDa subunit of alpha- and beta -Lv, respectively, and two peptides of the 30-kDa subunit of alpha- and beta -lipovitellin were determined and match those predicted from the gene for vitellogenin II, Vtg II. Compariso n of the amino acid composition of the 125- and 30-kDa subunits of alpha- a nd beta -lipovitellin support the conclusion that they originate from the s ame gene. The sequences of peptides from the 80- and 40-kDa subunits of alp ha -lipovitellin have not been found in the NCBI nonredundant data bank. Th e 27-amino acid N-terminal sequence of the 40-kDa protein is 56% similar to the last third of the Lv 1-coding region of the Vtg II gene, suggesting it may come from an analogous region of the Vtg I gene. We propose a scheme f or the precursor-product relationship of Vtg I.