cDNA sequence of lactophorin and and its emulsification function

乳蛋白（Lactophorin， LP）是牛乳蛋白酶-蛋白胨部分的主要糖蛋白，由两个主要的糖肽（27和17 kDa）组成。克隆了一段编码LP 27 kDa糖肽的cDNA （27kLP）。结果表明，该基因全长621 bp，编码信号肽18个氨基酸和成熟LP 135个氨基酸。推导出的成熟氨基酸序列与最近由Sorensen和Petersen化学测定的蛋白酶-蛋白氨酸组分3 （PPC3）相同[J]。乳业杂志，60,535,(1993)]。与经凝胶过滤分离的蛋白酶-蛋白胨组分-3 （PPC3）的其他组分相比，LP具有最高的乳化活性、乳化稳定性、比表面积和最小的中位直径。以1% LP和25%乳脂为原料制备的乳化液乳化活性为2500，具有较高的稳定性，其微球中位直径为2.45 μ m，比表面积为31.7 × 10^3cm^2/cm^3。当乳脂含量达到60 mg/g时，乳状液的乳化活性、乳化稳定性、比表面积和中位直径均有所提高。从疏水氨基酸残基在石蜡一级结构和二级结构α -螺旋轮中的分布情况讨论了石蜡的乳化能力。

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.