cDNA sequence of lactophorin and and its emulsification function

乳蛋白（LP）是牛乳蛋白酶-蛋白胨组分中的主要糖蛋白，由两种主要糖肽（27和17 kDa）组成。克隆了编码LP 27 kD糖肽的cDNA（27 kLP）。结果表明，该蛋白由621 bp组成，编码18个氨基酸的信号肽和135个氨基酸的成熟LP，推测的成熟氨基酸序列与Sorensen和Petersen最近化学测定的蛋白糖-蛋白胨组分3（PPC 3）的氨基酸序列相同[J.Dairy Res. 60，535，（1993）]。和比表面积和最小中位直径的小球相比，其他部分的蛋白酶-蛋白胨组分3（PPC 3）的凝胶过滤分离。由1%的LP和25%的乳脂制备的乳状液的乳化活性为2500，稳定性高，其颗粒的中值直径为2.45 μ m，比表面积为31.7 × 10^3cm^2/cm^3。此外，增加LP含量高达60毫克/克乳脂在乳液中增加乳化活性，乳液稳定性，比表面积和减少中值直径。从疏水氨基酸残基在LP一级结构和二级结构α-螺旋轮中的分布探讨了LP的乳化能力。

Lactophorin (LP) is a major glycoprotein in the proteose-peptone fraction of bovine milk and constituted of two major glycopeptides (27 and 17 kDa). A cDNA encoding 27 kDa glycopeptide of LP (27kLP) was cloned. It was revealed to consist of 621 bp, which encoded 18 amino acids for signal peptide and 135 amino acids for mature LP.The deduced mature amino acid sequence is identical to that of proteose-peptone component 3 (PPC3), which has recently been chemically determined by Sorensen and Petersen [J.Dairy Res.60,535, (1993)].LP had the highest emulsifying activity, emulsion stability, and specific surface areas and smallest median diameter of globules in comparison with those of other fractions of proteose-peptone component-3 (PPC3) separated by gel filtration. Emulsions prepared from 1% LP and 25% milk fat had 2500 of emulsifying activity and was highly stable and median diameter of their glubules was 2.45mum and their specific surface area was 31.7x10^3cm^2/cm^3. In addition, increasing of LP content up to 60 mg/g of milk fat in emulsion increased emulsifying activity, emulsion stability, and specific surface areas and decreased median diameter. Emulsifying ability of LP is discussed from the distribution of hydrophobic amino acid residues in the primary structure and in alpha-helical wheel of the secondary structure of LP.