Milk Folate Binding Protein Research Articles

Milk folate binding protein (FBP): A secretory protein for folate?

Analyses of human milk samples reveal that although folate binding protein (FBP) concentration varies considerably among individuals, a positive correlation with milk folate concentrations exists. The equation expressing this relationship is Y=29.2+0.78 X, where Y and X represent FBP and folate concentrations, respectively. Since folylpolglutamates comprise at least half of total milk folate and are known not to cross biological membranes, these data suggest that folate is likely to be secreted from the lactating cell as a complex with FBP. This complex could exit from the lactating cell by a route which is common to other milk proteins.

Neonatal role of milk folate-binding protein: studies on the course of digestion of goat's milk folate binder in the 6-d-old kid.

Groups of kids were reared from birth to 5 d on goat's milk. On the 6th day five of the kids received by bottle a morning feed of goat's milk with [3H]folic acid added to saturate the folate-binding proteins (FBP) (Expt 1); three kids received raw goat's milk containing only the endogenous folate and hence a large surplus folate-binding capacity (FBC) (Expt 2). The contents of the stomach, duodenum, jejunum and ileum were recovered by washing out 1.5 h after feeding (Expt 1) or at 0.5, 1 and 3.5 h after feeding (Expt 2). Recovery of [3H]folic acid 1.5 h after feeding (Expt 1) in all segments was 58.4%, mainly in a soluble form, most of this being in the stomach (37.0%) and ileum (14.3%). No surplus FBC was found in any gut segment. Sephadex G-75 chromatography of the soluble fractions of the contents of the various gut segments showed that [3H]folic acid remained bound to FBP throughout the stomach and small intestine. The bound [3H]folic acid exhibited a molecular weight of 81 000 in stomach contents, similar to that in the milk feed, presumably representing an aggregated form of the FBP, whereas in the intestinal contents its molecular weight was 39 000 indicating dissociation to monomer due to dilution in the recovery process. In Expt 2, the total recovery of free FBP in all four gut segments was 67, 54 and 23% respectively at 0.5, 1 and 3.5 h after the milk feed, and the distribution of FBP along the gut at 1 h was similar to that of [3H]folic acid-labelled FBP at 1.5 h in Expt 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophoretic and immunological properties of folate-binding protein isolated from bovine milk.

Changes of the folate-binding protein (FBP) concentration in bovine milk after parturition were investigated. The FBP was highly purified from mature milk by affinity chromatography. The purified FBP showed a single protein band in polyacrylamide gel electrophoresis and was immunologically homogenous in double immunodiffusion. However, in two-dimensional gel electrophoresis, the FBP was separated into several spots in isoelectric focusing in the first dimension, and each spot also showed two molecular weights in SDS-gel electrophoresis in the second dimension. But these FBP molecules were immunologically identical with each other. The neuraminidase treatment obviously diminished the number of isoelectric points of the FBP. Thus, the variety of FBP molecules was at least partially due to the variability of the sialic acid content in the carbohydrate moieties. Moreover, the milk FBP showed species-specificity among mammals immunologically as well as physicochemically.

100] Kinetics of folate-protein binding

Publisher Summary This chapter discusses the kinetics of folate-protein binding. In mammals, folate-(pteroylglutamate-)binding proteins have been demonstrated in cow's milk and human milk, hog kidney, rat liver, rabbit choroid plexus, intestinal brush border membrane from rat, leukemic cells, and in human serum and animal serum as well. Investigations of the kinetics of folate binding to protein need a method that separates protein-bound and free folate, without affecting the equilibrium between them. Adsorption of free folate to the charcoal method is predominant in the competitive radioassay methods for the determination of folate in serum where the folate-binding protein in milk has been used. It has the advantage of being quick and practical. However, it has many disadvantages: (1) in order to ensure that only free folate is bound to charcoal, the particles must be coated with various macromolecular substances, such as dextrane, albumin, or hemoglobin that act as a molecular sieve, (2) by ultrafiltration method, it is possible to obtain a good separation of free and bound folate if neither is bound to the membrane. The method has been used for investigating the binding of folate to milk protein and for an investigation of the binding of folate to serum proteins and to pure albumin preparations.

Effect of methotrexate on folate binding to a folate binding protein in cow's milk.

Folate in cow's milk was strongly bound to a minor whey protein. Methotrexate inhibited the folate binding in a log dosis dependent manner, but was a rather weak inhibitor. The binding mechanism of folate changed from a cooperative to a non-cooperative type in the presence of methotrexate. This model system could be used in investigations on human body fluids and tissues.

The folate-binding protein in milk

SummaryThe folate in cow's milk was strongly and specifically bound to a minor whey protein (FP), forming a complex of primary M of about 38000, but exhibiting concentration-dependent reversible aggregation. The binding protein was present in excess, and the milk had the capacity to bind about 50μgadded folic acid/l. An enriched concentrate of FP was prepared by ammonium sulphate fractionation—FP was precipitated at between 50 and 60% saturation—and further purified by chromatography in DEAE-cellulose and filtration in Sephadex gel G150. Its identity as a distinct minor whey protein was confirmed by comparative starch gel electrophoresis at various pH values.Some properties of the protein are described, and its physiological significance discussed.