Nomemclature of the proteins of cow's milk: fourth revision

Cross-reactive idiotypes in immunoglobulin A-deficient sera

Mice of inbred strains immunized with simple antigens can produce antibodies that share similar V regions, which result in serologic similarities called cross-reactive idiotypes (CRI). In this study, we considered the possibility that IgA-deficient humans, who are continuously immunized via the intestinal tract by dietary protein, might also produce antibodies sharing CRI. For this, anti-casein antibodies were isolated from the blood of 16 adult IgA-deficient donors (4 Finns and 12 North Americans) and an autologous anti-anti-casein from the blood of one of the Finnish donors. In addition, a heterologous anti-anti-casein was raised to the casein-anti-casein immune complexes of this donor. Comparing the activities of the two anti-idiotypes, it was found that both bind anti-casein in the region of the antigen binding site, but that each binds additional determinants not located within this region, with the heterologous reagent having more affinity for these latter determinants than the autologous anti-idiotype. Using both reagents in enzyme-linked immunosorbent assay inhibition assays, extensive cross-reactivities between anti-caseins were demonstrated. Using the autologous anti-idiotype, 5 of 16 anti-caseins were found to share CRI, and with the heterologous reagent 12 of 16 shared CRI. In both assays, the anti-caseins of Finnish donors displayed more cross-reactivity than those derived from Northern American donors. These studies show that specific, commonly shared CRI can be identified in this human system in which antibodies are raised as a result of natural immunization across the gastrointestinal mucosa.

Food allergy and intolerance

This article focuses on intolerance to food proteins, discussing the definition and history of food intolerance, the basics of gastrointestinal mucosal immunity, specific food antigens, pathogenesis, clinical manifestations, as well as diagnosis, therapy, and prevention.

[Analysis of proteins in food with electrophoretic and chromatographic methods]

The efficiency of electrophoretic methods (gel electrophoresis, isoelectric focusing, twodimensional techniques) and of chromatographic methods (size exclusion and ion exchange chromatography, reversed phase HPLC) to analyze proteins in foods is reviewed. Several selected applications are discussed in detail. The large diversity of proteins in a particular food results in a unique electrophoretic or chromatographic pattern, that can be used for identification purposes, by means of the so called indicator proteins. The adaptability and resolving power of the methods assure their extended application to many protein containing foods. The uniqueness of the patterns obtained warranties differentiations of even closely related animal or plant foods as well as mixtures of them. The methods also allow quantitative determinations of mixtures of foods. Their ease of handling and good reproducibility and reliability favours their use in routine analyses. Numerous investigations on fish, meat and derived products, non-meat proteins in meat products, milk, cheese, cereals and products made of cereals, oilseed proteins, legumes, fruits and vegetables described in the literature are here presented.

Determination of tryptophan as the reduced derivative by acid hydrolysis and chromatography

A new procedure for the analyses of tryptophan and the total amino acid composition of proteins was based on the observations that pyridine borane reduces tryptophan in trifluoroacetic acid, while other amino acids remain intact [M. Kurata, Y. Kikugawa, T. Kuwae, I. Koyama, and T. Takagi (1980) Chem. Pharm. Bull. 28, 2274-2275; W.S.D. Wong, D.T. Osuga, and R.E. Feeney (1984) Anal. Biochem. 139, 58-67]. Concentrated HCl was used instead of trifluoroacetic acid for analytical purposes. The products were stable to hydrolysis in 6 N HCl, and the reduction did not interfere with hydrolysis and subsequent analyses. Quantitative recovery was achieved with most proteins when they were subjected to acid reduction in ice-cooled concentrated HCl with two incremental additions of pyridine borane. The reaction was terminated after 10 min by dilution with an equal volume of H2O, vacuum sealing, and hydrolyzing at 110 degrees C for 22 h. The yields of the expected values for cytochrome c, catalase, bovine serum albumin, subtilisin BPN', trypsin, chymotrypsin, beta-lactoglobulin, lysozyme, and pepsin were obtained. Ovotransferrin and ovalbumin, however, yielded values for tryptophan lower than literature values. With two different ion-exchange methods, the recoveries of all other amino acids were comparable to those obtained by acid hydrolysis with 6 N HCl. Since the same hydrolysate can be analyzed for both tryptophan and all the other amino acids, the procedure is a more convenient method than those requiring separate determinations. Initial results indicate that the method may be applied to high-performance liquid chromatographic procedures with adaptations of the protocols if necessary.

Determination of partial specific volume and absolute concentration by densimetry

The apparent partial specific volume, phi, of a protein (or other macromolecule) and the absolute concentration, c, can be determined from the densimetry of solutions and diffusates in 1H2O , 2H2O and 1H2O/2H2O mixtures if the ratios of concentrations (relative concentrations) are known. The densimetry method allows a non-destructive check on total macromolecule concentrations without prior knowledge of specific u.v.-absorption coefficient. The method may be especially useful in small-angle neutron-scattering studies.

[The quantitative determination of protein content in milk by means of ultraviolet spectrophotometry. 2. The suitability of the difference of absorbance at 235 and 280 nm for quantitative milk protein analysis]

The protein content of skimmed milk was determined by measuring the absorbance at 235 and 280 nm after dilution with alkylpolyglycolethersulphate solution. The difference of absorbance A235-A280 shows a high correlation to the values of KJELDAHL nitrogen analysis (r = 0.99). The protein content of casein and milkserum solutions could be determined in the same way. The method has the advantage, that their results are approximately independent of the amino acid composition of proteins, the content of nucleic acids, salts, lactose and non protein nitrogen. Both absorbances are obtainable from one solution. The dependence of the absorbance difference from the age of solution, the age of milk and from the temperature was investigated as well as the influence of preservatives.

Determination of native and denatured milk proteins by high-performance size exclusion chromatography

High-performance size exclusion chromatography on a TSK 3000 SW column was used to separate and quantify the individual milk proteins in their native and/or denatured state. Quantitation of the individual native whey proteins within +/- 10% was achieved. The denatured proteins were dissociated into their monomer units by using sodium dodecyl sulphate and beta-mercaptoethanol. A good separation of the whey protein monomers was achieved and the quantitation of the individual whey proteins within +/- 10% was possible. Under these conditions, alpha s1- and beta-casein were eluted as one peak, whereas kappa-casein and gamma-casein were eluted in the same position as beta-lactoglobulin and alpha-lactalbumin respectively. A method for calculating the areas and hence the concentration of the individual proteins in a mixture of casein and whey proteins is described.

Fractionation of a whey growth factor for Streptococcus agalactiae into two active components containing proteins

Previously three factors (F-1, F-2, F-3) that stimulated in vitro growth of Streptococcus agalactiae were separated from wheys of milk and colostrum by chromatographic procedures. Now F-1 was separated further into two active components, F-1a and F-1b, when rechromatographed on an anion exchange resin with distilled water as eluent. The stimulatory activity was associated with two protein peaks whereas a third protein peak that was eluted in those fractions containing lactose was not stimulatory. Most of the stimulatory activity (76 to 80%) and protein (90 to 93%) were retained by a filter with retention of greater than 1,000 MW. Two stimulatory factors were confirmed by separation of F-1 fractions by step-gradient elution on a column of octadecylsilica; one protein peak was found for each of the three solvents. Samples with protein eluted with .1 N formic acid and formic acid: methanol (1:1) had stimulatory activity, whereas the sample with protein eluted with 100% methanol was inactive. Results were similar when F-1 fractions were applied to Sep-Pak (muBondapack C18) cartridges and eluted with water, 50% methanol, and 100% methanol. Proteins in the Sep-Pak eluates with stimulatory activity (water and 50% methanol) were heterogeneous and different when separated by high-voltage paper electrophoresis. Proteose-peptone preparations with added lactose were chromatographed on columns of anion exchange resin, with distilled water as eluent, and produced two peaks of protein with elution volumes comparable to peaks 1 and 3. Lactose appeared to be a major factor in eluting the second protein peak.(ABSTRACT TRUNCATED AT 250 WORDS)

Age and previous lactations as factors in the amount of bovine colostral immunoglobulins

Blood and colostrum samples were obtained from 87 dairy cows in five lactation groups and analyzed for immunoglobulins G1, G2, M, and A. The five groups ranged from cows in first lactation, about 30 mo of age, to cows in fifth or more lactation, about 84 mo of age. Compared to older groups, blood serum of cows in first lactation contained less G1. Cows in first lactation also produced less total colostrum containing less total G1, G2, and M. Immunoglobulin G1 comprised over two-thirds of the immunoglobulins in the colostrum of all groups. Older cows had more immunoglobulin G1 in their colostrum with a tendency toward a higher ratio of G1 to G2. Amount of immunoglobulin A was constant through all lactations. After a rise in the second lactation, total amount of immunoglobulins G2 and M tended to level off. Total immunoglobulin G1 tended to reach a maximum in the third or fourth lactation, almost doubling in amount compared to the first lactation. Age and number of lactations are factors correlated with amounts of these immunoglobulins in colostrum.

Isolation and solubilization of casein kinase from Golgi apparatus of bovine mammary gland and phosphorylation of peptides

Phosphate incorporation from [gamma-32P]ATP into native and dephosphorylated alpha s1-casein is catalyzed by a casein kinase localized in the Golgi apparatus of lactating bovine mammary gland. Casein kinase from the Golgi is activated with either Mg2+ or Ca2+, and increased specific activity is observed with dephosphorylated casein as the substrate. The casein kinase can be solubilized from Golgi apparatus by the non-ionic detergent, Triton X-100. Gel permeation chromatography on Sepharose CL-4B yields a Stokes radius of 10 nm for the detergent-solubilized casein kinase. Dephosphorylated beta-peptide, the amino-terminal peptide from beta-casein, is a good substrate for the solubilized casein kinase. With dephosphorylated beta-peptide, the maximal velocity is 9.1 and 12.0 nmol/min per mg protein with Mg2+ and Ca2+ activation, respectively. The Michaelis constant for beta-peptide is greater with Ca2+ than with Mg2+ (4.8 mg/ml compared to 0.97 mg/ml). However, the Michaelis constant for ATP is not greatly influenced by these metal ions. The Triton X-100-solubilized Golgi enzyme can also catalyze the phosphorylation of peptides, such as fibrinopeptide A and alpha-melanocyte stimulating hormone.

Isolation and characterization of beta- and gamma-caseins from horse milk

Three groups of casein components were isolated from horse milk. Group I is almost insoluble at acid and neutral pH, and is rather heterogeneous on alkaline gels with or without sodium dodecyl sulphate. Group II shows strong similarity to beta-casein from other species, as concluded from its amino acid composition and its N- and C-terminal sequences. This group consists of five electrophoretically distinguishable forms, all containing ester phosphate groups but no carbohydrate. Group III is composed of C-terminal fragments of the beta-like (group II) fraction and probably arises from the action of a plasmin-like enzyme present in horse milk. It does not contain phosphate or carbohydrate. Homology of this group with bovine gamma-caseins is demonstrated. Both beta- and gamma-like caseins are more soluble at 4 degrees C than at room temperature.

The identification of specific antigens in circulating immune complexes by an enzyme-linked immunosorbent assay: detection of bovine kappa-casein IgG complexes in human sera

Circulating immune complexes have been implicated in the development of tissue injury in many chronic disease states, but in most instances the inciting antigens have not been identified. This report describes the development of a sensitive enzyme-linked immunosorbent assay which can be used to screen rapidly and simultaneously the immune complexes of numerous sera for the presence of a suspected antigen. The prototype antigen sought here was kappa-casein, a frequent participant in immune complex formation in IgA deficiency and in atopic diseases. The enzyme-antibody conjugate described here can detect as little as 0.11 ng/ml of kappa-casein; for immune complexes formed in vivo or in vitro, one can distinguish circulating complexes containing casein from complexes not containing this antigen. Using this reagent, a major antigen in the immune complexes of hypogamma-globulinemic patients treated with intravenous gamma-globulin was unexpectedly identified as kappa-casein. This method of specific immune complex analysis is suggested as a practical and effective approach to the elucidation of the antigenic constituents of immune complexes found in many diseases.

Purification and properties of a major casein component of rat milk

A casein component (C2-casein) was purified by ion-exchange and gel filtration chromatography from rat milk, and the properties of this protein were examined. The molecular weight of C2-casein, as determined by Sepharose 4B gel filtration in 6 M guanidine hydrochloride, was 34 000 +/- 1000. The average hydrophobicity calculated from the amino acid composition showed that C2-casein is a rather hydrophilic protein. The alpha-helix content obtained from optical rotatory dispersion experiments was about 12%. In ultracentrifugation analyses, monomer and polymer peaks of C2-casein were both seen, and the monomer-to-polymer ratio was not affected by changing temperature conditions. C2-casein was precipitated by the presence of 2.5 mM CaCl2, and the precipitability was greatly decreased by the dephosphorylation of the protein. C2-casein was stabilized from Ca2+-dependent precipitation by the addition of another rat casein component (C3-casein) or of bovine kappa-casein.

Phosphorylation of caseins, present evidence for an amino acid triplet code posttranslationally recognized by specific kinases

The fifty of so phosphorylated hydroxyamino acid residues hitherto investigated in caseins from different species have been found to occur in tripeptide sequences -Ser/Thr-X-A- where X represents any amino acid residue and A is an acidic residue. This strongly suggests that phosphorylation of caseins involves basically the stepwise enzymatic recognition of primary and secondary anionic amino acid triplets where the determinants are dicarboxylic residues and phosphoseryl residues, respectively. Studies of genetic variants of bovine caseins have provided clear-cut evidence for the actual occurrence of the former recognition sites. The occurrence of the above tripeptide sequences is a necessary but not a sufficient condition for phosphorylation of caseins to occur. Possible factors of constraint such as different intrinsic properties of both phosphate acceptor residues and acidic determinants, the characteristics of the local environment in terms of overall charge and hydrophilicity, secondary structure and steric hindrance, an insufficient available pool of casein kinase(s)... are discussed. All evidence now available supports the concept that phosphorylation of caseins is a posttranslational event and it is suggested that the process may occur during the transfer of completed polypeptide chains from the smooth endoplasmic reticulum to the Golgi apparatus where most of phosphate incorporation is presumably carried out. This organelle is rich in membrane-bound specific cyclic AMP-independent kinase(s) able in vitro to rephosphorylate specifically although not completely phosphatase-treated caseins and caseinophosphopeptides.

14C-Methylated beta-casein as a substrate for plasmin, and its application to the study of milk protein transformations

A method was investigated for the sensitive radiochemical assay of milk protein transformations. beta-Casein was reductively methylated with NaBH4 and H14CHO giving a product of spec. act. 4.42 microCi/mg in which a maximum of 12% of the lysine residues were labelled. Methylation did not alter the electrophoretic or chromatographic properties of the protein, or its pattern of proteolysis by plasmin. The substrate susceptibility of 14C-methylated beta-casein towards plasmin was determined by measuring radioactivity transfer to the proteolytic fragments gamma 2- and gamma 3-casein. Compared with the native protein, no decrease in substrate susceptibility was detected. The presence in milk of the plasmin-like enzyme, milk proteinase, was demonstrated and its activity at 4 degrees C was quantified by examination of the fragmentation pattern of added 14C-methylated beta-casein. It was concluded that 14C-methylated protein substrates, prepared by reductive methylation, are well suited to the study of hydrolytic enzymes and that they can provide valuable information on milk protein transformations. In particular, no interference was encountered with the rate of cleavage by plasmin when the level of methylation was kept to a minimum.

Immunoglobulin production and transport by the mammary gland

In origin immunoglobulins in mammary secretions are both humoral, arising from the blood stream, and local, arising from production by plasmacytes in the mammary gland. The relative importance of each of these sources varies between species. In some species (human, rabbit, etc.), the transfer of maternal immunoglobulins to the blood stream of the neonate occurs in utero across the placenta or yolk sac membrane. In other species, including ruminants, transfer of maternal immunoglobulins to the neonate occurs exclusively via the colostrum. Both in utero and colostral routes of transfer are operative in other species. The concentration and class of immunoglobulins in the colostrum and milk of a species reflect the route and origin of the immunoglobulins. Immunoglobulins transferred in quantity in utero or via the colostrum are mainly of the IgG class. Immunoglobulins locally produced by plasmacytes located adjacent to the secretory epithelium and in the mammary secretions are largely of the IgA and IgM classes. The bovine transfers large amounts of IgG immunoglobulins, and IgG1 in particular, from the blood stream across the mammary barrier into colostrum (and milk) by a specific transport mechanism. Bovine colostrum and milk also contain much smaller amounts of locally produced IgA and IgM.

Two-dimensional separation of human body fluid proteins

High resolution protein patterns of various human body fluids are compared. They were obtained by non-restrictive agarose electrophoresis in the first and exclusion electrophoresis on polyacrylamide pore gradients in the second dimension. The majority of serum proteins above 10 mg/dl have been identified and the heterogeneities of high density lipoproteins, immunoglobulins and haptoglobins become visible within the charge/size grid of the two-dimensional pattern. Since secretory and serum-derived components can be differentiated, the contribution of protein synthesis and filtration to the formation of the finally released fluid can be assessed. The technique may be used to screen complex soluble protein mixtures for pathological components. There is a wide range of variations in composition from the secretory fluids (e.g. tears, colostrum, milk, seminal fluid) to virtually "pure" filtrates (pleural effusions, osteoarthritic synovial fluid, cyst puncture fluid, and amniotic fluid). It is evident that the composition of the serum-derived fraction depends primarily upon the selectivity of the respective blood/body fluid barriers. The resolution capacity of the technique is compared with that obtained by two-dimensional gel-focusing/SDS electrophoresis of the constituent serum protein subunits.

Selective IgA deficiency and circulating immune complexes containing bovine proteins in a child with chronic graft versus host disease

We have previously shown that a selective absence of serum and secretory immunoglobulin A (IgA) may lead to the development of circulating immune complexes which appear to contain bovine milk antigens. We report here that high levels of circulating immune complexes were found in the serum of a child who was treated for severe combined immunodeficiency by bone marrow transplantation but in whom the IgA-producing cells subsequently failed. As increasing amounts of complexes appeared over a two year period, the child had a parallel progression of an apparent chronic graft versus host disease including a Sjögrens syndrome and scleroderma. Very large amounts of complexes were eventually formed but the level fell 77 per cent after milk was excluded from the diet. Chemical studies on the complexes showed that the majority of complexes did contain bovine milk proteins, and fluorescence antibody staining of skin biopsy samples showed the presence of dense deposits of bovine casein in the dermis. The relationship between bovine protein-antigen antibody complexes and the chronic graft reaction remains uncertain.