Identification and purification of apolipoprotein C-III from the serum of cows

To identify, purify, and analyze distribution of apolipoprotein C-III in lipoprotein fractions and to evaluate its concentration in serum from calves, heifers, and cows during various stages of lactation.

Sera from 3 female calves, 3 heifers, and 12 cows during early, middle, late, and nonlactation stages.

Apolipoprotein C-III was identified by use of amino-terminal amino acid sequence analysis of bands separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Purification was performed by extraction with acetone, delipidation with 2-propanol, and 2 chromatographic steps. The apolipoprotein C-III concentration in the total lipoprotein fraction was evaluated by densitometric scanning of the bands for apolipoprotein C-III separated by electrophoresis, using purified apolipoprotein C-III as an internal standard.

Apolipoprotein C-III was identified as 8.2- and 7.3-kd proteins with identical amino acid sequences. The 2 proteins were mainly found in the high-density lipoprotein fraction, then were purified separately. Serum apolipoprotein C-III concentration was significantly (P < 0.05) higher in cows during lactation than in nonlactating cows and was negatively correlated with serum triglyceride concentration (r = -0.620, P < 0.01).

The role of apolipoprotein C-III in cows may involve a function related to lactation.