Changes in the Protein Fractions of Human Milk during Lactation

Abstract

The changes in the absolute and relative contents of α- and ĸ-caseins, lactoferrin, α-lactalbumin, serum albumin and lysozyme in human milk have been studied through the period of lactation. Protein fractions of 209 samples were analyzed by a discontinuous poly-acrylamide gel electrophoresis method, β- and ĸ -caseins decreased from colostrum to mature milk although their relative percentages remained constant. They accounted for 12–15 and 9–13% of the total protein in human milk, respectively. Lactoferrin decreased in absolute and relative amounts with advancing lactation. This protein represented 32–19% of the human milk proteins. α-Lactalbumin slightly decreased from colostrum to transitional milk but there was an increase in mature milk by 16–30 days. The percentages of this protein in colostrum and mature milk were approximately 23 and 30%, respectively. Serum albumin also decreased with advancing lactation, but the differences between transitional and mature milk were not statistically significant. Lysozyme increased from colostrum to mature milk both in relative and absolute amounts. Colostrum contained about 262 µg/ml, and mature milk 1,246 µg/ml, representing 1.5 and 12.1% of total milk proteins.

Measurement of nine human milk proteins by nephelometric immunoassays: application to the determination of mature milk protein profile

“…Recovery studies showed close agreement between the theoretical and measured protein concentrations in dilution-overloadind assays (linear recovery on large ranges of concentrations with mean percentage very close to 100%). Results of the measurements of nine proteins performed together in a great number of human mature milk samples are, for the most part, in good agreement with those previously reported in past years (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14), using different techniques and, the most often, restricted to the determination of the one or another of these proteins. Emergence of new analytical procedures in the late years, such as conventional or microparticleenhanced immunonephelometry, today allows major proteins of human milk to be analyzed with sensitivity, easiness, and singleness of methodologies.…”

“…Among these components, milk-specific and plasma proteins, such as beta-casein (␤-CN), kappacasein (-CN), alpha-lactalbumin (␣-LA), serum albumin (SA), lactoferrin (LF), lysozyme (LZ), immunoglobulins A (IgA), C3, and C4 complement fractions have important nutritious and immunological functions. Numerous methods, such as fast protein liquid chromatography (2,3), polyacrylamide gel electrophoresis (4,5), ion-exchange chromatography (6), enzyme activity measurement (7), and various types of immunoassays (8 -14), have been reported to assay these proteins in human milk. Most of these techniques lack sensitivity and moreover require sample pretreatment or long incubation periods.…”

Isolation of a lactoferrin cDNA clone and its expression in human breast cancer

“…The J16 clone is homologous to the 3' terminus of the lactoferrin sequence, which encodes a single glycosylated polypeptide of -70-80,000 Mr (Teng et al, 1986) which like transferrin has iron binding properties, and has been found in human (Sanchez-Pozo et al, 1986;Hegnhj et al, 1986) exocrine secretions, and has been isolated from milk and neutrophilic leucocytes (Moguilevsky et al, 1985). A mouse cDNA clone was isolated form a uterine lambda gtl 1 library by immunoscreening and was found to have -70% homology with the human sequence (Metz-Boutigue et al, 1984) recently cloned from a myeloid library using an oligonucleotide (Rado et al, 1987).…”

Influence of the Mother’s Weight and Socioeconomic Status on the Fatty Acid Composition of Human Milk

“…A parallel study was simultaneously car ried out to examine the changes in the pro tein fractions o f human milk during lactation [19].…”