Galactolipid formation in chloroplast envelopes. I. Evidence for two mechanisms in galactosylation

Bovine and human thyroxine-binding globulin were purified from serum by a three-step purification procedure which comprised affinity chromatography consecutively on thyroxine- and Concanavalin A--Sepharose and finally preparative polyacrylamide gel electrophoresis. The molecular weights of the two proteins were similar (54 000) as well as their carbohydrate contents while some differences in amino acid composition were found. Rabbit antiserum against bovine thyroxine-binding globulin reacted with human thyroxine-binding globulin with no sign of spur formation.     

Gas chromatographic determination of E prostaglandins in human amniotic fluid

A simple procedure is described for the extraction and purification of prostaglandins from amniotic fluid. Combined with gas chromatography with electron-capture detection, this provides a rapid and specific method for the determination of PGE in human amniotic fluid.     

A simple two-step purification of human and monkey alpha fetoprotein from amniotic fluid and serum.

We developed a two-step purification system to characterize alpha fetoprotein (AFP) in early gestation amniotic fluid and late gestation fetal serum or cord blood from monkey and human. It involves only two chromatographic steps, allows preparative purification using up to 12 ml of starting sample, can purify up to 350 micrograms of AFP at one time, and can be used to purify both fetal serum or amniotic fluid AFP from two different species. This procedure will allow detailed biochemical analysis of purified AFP from different stages of fetal development.     

Plasma thyroxine-binding proteins and thyroid hormone levels in primate species; is callithricidae thyroid hormone resistant?

Thyroxine(T4)-binding to serum proteins in primates; catarrhini, prosimiae, and platyrrhini were studied by polyacrylamide gel electrophoresis T4 binding analysis. From the electrophoretic analysis, it was shown that thyroxine-binding proteins similar to human thyroxine-binding globulin (TBG) and thyroxine-binding prealbumin (TBPA) were present in catarrhini and prosimiae species, but not in platyrrhini (callithricidae and cebidae). T4-binding analysis also revealed that catarrhini and prosimiae have a high affinity T4-binding protein similar to human TBG. The association constant (Ka) for T4 of the plasma proteins in these species was approximately 2.0 X 10(10) M-1. On the other hand, it was unable to demonstrate a high affinity binding site for T4 in the plasma of platyrrhini species. Both the total and free thyroid hormone concentrations in catarrhini and prosimiae were similar to those in human. Total T4 in cebidae, one of the platyrrhini species, was extremely low. Among 8 animals examined, T4 in 6 was undetectable by radioimmunoassay and the mean T4 of the other two was 2.8 micrograms/dl. However, free thyroid hormone concentrations were similar to those in human. In callithricidae, another platyrrhini species, T4 in plasma was 6.90 +/- 2.11, which is comparable to the level in normal human subjects. However, in this species, high-affinity T4-binding protein was lacking and free thyroid hormone concentrations were extremely high (most were higher than the assay limit). Although the thyroid function of callithricidae remains to be studied, it will be interesting if callithricidae is resistant to thyroid hormone action.     

Effect of structural changes in thyroxine-binding globulin on its biological activity and immunochemical properties

Using spectroscopic, electrophoretic and microcalorimetric techniques, the changes in the spatial structure of human thyroxine-binding globulin (TBG) induced by exposure of protein solutions to high temperatures (45-90 degrees C) and low pH (2.5-6.0) were studied. Simultaneously the biological activity and immunoreactivity of TBG samples were measured. The structural changes were manifested at 52 degrees C or at pH 4.0 and were then aggravated with a rise in temperature or a decrease of pH. The circular dichroism spectra showed that the molecular ellipticity had a maximum decrease (by 10%) at 218-222 nm. In fluorescence spectra excitable at 280 nm the band half-width increased by 4-6 nm; their intensity decreased by 30-40%, whereas the position of the maxima did not change significantly. After addition of an equimolar amount of thyroxine to inactivated TBG the protein fluorescence was quenched by 25-40%. The electrophoregrams of treated preparations contained additional protein bands possessing no biological activity, whose mobility was less than that of native TBG. Microcalorimetric assays of native TBG revealed a thermoabsorption peak with a maximum at 62.5 degrees C and a half-width of 7.1 degrees C. The thermodynamic parameters of melting of TBG spatial structure were consistent with a model of a two-domain structure of the molecule. The biological activity and immunoreactivity of TBG showed a coordinated decrease with a rise in the degree of protein denaturation, However, the formation of TBG complex with antibodies did not screen the thyroxine-binding center of TBG and did not alter its affinity. Possible mechanisms of structural transition of TBG and its effect on the biological properties of TBG are discussed.     

Concentration of thyroxine-binding globulin: value of direct assay.

The concentration of thyroxine-binding globulin (TBG) in the serum can now be measured by direct assays that are simple and inexpensive. Comparison of a direct measurement of TBG concentration with a widely used indirect method (Thyopac-3) showed that the indirect method was inaccurate when TBG concentrations were high. This will result in an increase in the derived free thyroxine index (FTI), so that euthyroid patients with a raised TBG concentration may be at risk of being labelled thyrotoxic. Correction of serum total thyroxine (T4) concentration according to the actual TBG concentration (T4:TBG ratio) provided a better correlation with thyroid state than FTI.     

Molecular cloning and primary structure of rat thyroxine-binding globulin

Rat thyroxine-binding globulin (TBG) cDNAs were isolated from a rat liver cDNA library by using a human TBG cDNA as a probe. From two overlapping cDNA inserts, an aligned cDNA sequence of 1714 nucleotides was obtained. There was 70% homology with human TBG cDNA over the span of 1526 nucleotides. In order to confirm that the cloned cDNA encodes rat TBG and to localize the NH2-terminal amino acid of the mature molecule, the protein was purified by affinity chromatography and subjected to direct protein microsequencing. The NH2-terminal amino acid sequence was identical with that deduced from the nucleotide sequence. The rat TBG cDNA sequenced consisted of a truncated leader sequence (35 nucleotides), the complete sequence encoding the mature protein (1194 nucleotides) and the 3'-untranslated region (485 nucleotides), containing two polyadenylation signals. It was deduced that rat TBG consists of 398 amino acids (Mr = 44,607), three NH2-terminal residues more than human TBG, with which it shares 76% homology in primary structure. Of the six potential N-glycosylation sites, four are located in conserved positions compared to human TBG. Northern blot analysis of rat liver revealed an approximately 1.8-kilobase TBG mRNA. Its amount increased markedly following thyroidectomy and decreased with thyroxine treatment in a dose-dependent manner.     

Comparative characteristics of molecular forms of human thyroxine-binding globulin

Two molecular variants, of thyroxin-binding globulin (TBG), TBG-1 and TBG-2, were obtained from human retroplacental blood by fractionation of pure TBG on concanavalin A-Sepharose. It was found that both variants are immunologically identical, have similar molecular weights, amino acid composition and spectral properties, and possess the same affinity for thyroid hormones. However, TBG-1 and TBG-2 differed in charge upon isoelectrofocusing and had different monosaccharide composition. The existence of two molecular variants of TBG in pregnancy is probably due to the peculiarities of the polypeptide chain glycosylation during TBG biosynthesis.     

Purification of a high molecular weight somatomedin binding protein from human plasma

The somatomedins insulin-like growth factor I and II (1,2) are in serum bound to high-molecular weight binding proteins (6,7,8). By use of a four step chromatographic procedure a somatomedin binding protein was isolated from outdated human plasma. Exclusion chromatography on Sephadex G-200 disclosed a molecular weight of 150 kDa. After lyophilization however, the binding activity was found in a lower molecular weight range of 35-45 kDa. A partial amino acid sequence analysis of the lyophilized material revealed a possible N-terminal sequence of Ala-Pro-Trp. This sequence is identical to the N-terminal sequence of the 35 kDa somatomedin binding protein previously isolated from human amniotic fluid (16).     

Comparison of human thyroxine-binding globulin purification by affinity chromatography procedures

Three procedures for the isolation of thyroxine-binding globulin from human serum, using affinity chromatography on triiodothyronine (T3) linked to Sepharose (A), thyroxine (T4) linked to Sepharose (B) or T3 linked to epoxy-Sepharose (C) as the first purification step, were compared. With the use of additional purification steps, the three procedures yielded pure thyroxine-binding globulin without desialylation. With procedure A, the initial binding of T4-binding globulin to T3-Sepharose was very low, yielding a poor final recovery (17%). Procedure B gave the highest yield (35%) after a three-step purification, with a low T4 content (0.15-0.30 mol/mol). Procedure C also gave a high yield (28%) after only two purification steps, with a T4 content greater than 0.7 mol/mol. The microheterogeneity of T4-binding globulin obtained with these three procedures was demonstrated by isoelectric focusing: five major bands were observed between pH 4.1 and 4.6, and intermediate faint bands (often doublets) in the same pH range. However, with procedures A and C, the most acidic bands (pH 4.10-4.20) were always absent. Thyroxine-binding globulin was preincubated with radioactively labelled T3 or T4 and the hormone-protein complex was analyzed by isoelectric focusing. The binding of T3--compared to that of T4--was reduced in the most acidic protein subspecies. These results suggest differences in the thyroid hormone binding properties of the various subspecies of human T4-binding globulin.     

A high-capacity hydrophobic adsorbent for human serum albumin

A simple method, based on salting out hydrophobic interaction chromatography, for the efficient removal of trace amounts of serum albumin from partially purified protein preparations is described. The method is also successfully applied for the purification of albumin from Cohn fraction IV, a by-product obtained from the commercial fractionation of human serum proteins by the ethanol precipitation procedure. About 70% of the adsorbed albumin can be eluted by buffer of low ionic strength and can thus be lyophilized directly, if required. The adsorbent can be used for several cycles of adsorption and desorption without affecting its selectivity or capacity. Its adsorption properties and capacity for serum albumin are compared with those of the commercially available adsorbent Blue Sepharose CL-6B.     

Binding of thyroid hormones and their analogues to thyroxine-binding globulin in human serum.

The present study was undertaken to study the binding of several thyroid hormones and structurally related compounds to human serum thyroxine-binding alpha-globulin (TBG). The source of TBG was normal human serum diluted 1:100 in 0.035 M barbital buffer, pH 7.4. In the binding assays, 125I-thyroxine, unlabeled thyroxine, and diluted serum were incubated for 20 h at 37 degrees in Plexiglas equilibrium dialysis units. Two orders of binding sites were discerned: a high affinity, low capacity binding site with an affinity constant of approximately 2.5 X 10(9) M-1, and a low affinity, very high capacity binding site with an affinity constant of less than 10(6) M-1. Studies with purified TBG, serum deficient in TBG, and purified human serum albumin indicated that the high affinity site represented binding to TBG and the low affinity site represented binging to albumin. The ability of several groups of thyroid hormone analogues to bind to TBG was then investigated. As a result of these studies, the following structural features of thyroid hormones were found to be important for optimal binding activity: (a) the L-alanine side chain conformation, (b) the presence of a 4'-hydroxyl group, (c) the presence of two substituents in the inner and outer rings (positions 3, 5, 3', and 5'), and (d) the presence of either bromines or iodines in the inner ring and iodines in the outer ring. Of lesser importance was the presence of an oxygen atom in the ether position.     

The charge heterogeneity of soluble human galactosyltransferases isolated from milk, amniotic fluid and malignant ascites.

UDP-galactose: N-acetylglucosamine galactosyltransferase was isolated from pooled human milk, pooled amniotic fluid and from two different individual samples of malignant ascites. The purification procedure involving two successive affinity chromatography steps on N-acetylglucosamine--agarose and alpha-lactalbumin--agarose yielded an enzyme preparation homogeneous by size. Under non-denaturing conditions the ascites and amniotic fluid enzymes had identical electrophoretic mobility, but they moved faster than the milk enzyme. Isoelectric analysis in the presence and absence of urea resolved the milk enzyme into at least 13 different forms, nine of which had the same isoelectric points after refocusing. All enzyme forms showed similar activity when free N-acetylglucosamine, ovalbumin, sialic-acid-free ovine submaxillary mucin and glucose, in the presence of alpha-lactalbumin, were used as acceptor substrates. Comparative isoelectric focusing of the three galactosyltransferases revealed identical patterns of the amniotic and ascites enzymes, but only partial overlap with the milk enzyme, which was less negatively charged. Neuraminidase treatment of ascites and milk galactosyltransferases produced very similar focusing patterns. The possible structural basis for this charge heterogeneity is briefly discussed.     

Affinity chromatography of thyroxine-binding proteins from human serum

The affinity matrix prepared by the attachment of L-thyroxine (T4) to epichlorohydrine-activated Sepharose 4B biospecifically absorbs the T4-binding globulin (TBG), 25K and 80/27K proteins, immunoglobulin G (IgG) and albumin (HSA) from human normal and retroplacental sera. The absorbed protein patterns were shown to depend on the immobilized T4 concentration, pH, temperature and incubation time. The potent eluents desorbing 85-100% of the protein are 1 mM NaOH, 3 M NH4SCN, 10(-5) M T4 or 3 mM 8-anilinonaphthalene-1-sulfonic acid (ANS) for TBG; NaOH, NH4SCN, 3 mM MgCl2 or 12mM sodium cholate for 25K protein and HSA; NaOH, NH4SCN or MgCl2 for the 80/27K and 25K proteins and IgG. Moreover, T4 desorbs small amounts (6-8%) of the 80/27K and 25K proteins, while sodium cholate elutes about 6% of TBG. The eluted from T4-Sepharose 4B and further purified TBG, 25K and 80/27K proteins display different [125I]T4-binding activities within the pH range from 2 to 9 and differ by their resistance to thermal inactivation at 50-80 degrees C. Double radial immunodiffusion analysis with the use of antisera to TBG, 25K, 80/27K, HSA and IgG demonstrated that the proteins share no common antigenic determinants. It was concluded that the novel 25K and 80/27K proteins represent endogenous components of the human blood thyroid hormone-binding protein system rather than fragments or aggregates of the known T4-binding proteins.     

A simple procedure for the purification of rat alpha-fetoprotein

A simple purification procedure for obtaining a high yield of electrophoretically and immunologically pure rat α-fetoprotein from amniotic fluid is described. Rat amniotic fluid is passed through an anti-rat albumin immunoabsorbent column to remove albumin. The albumin-free eluate is then chromatographed on DEAE-Sephacel to separate α-fetoprotein from transferrin and other minor protein contaminants. This two-step purification procedure results in a recovery of approximately 70% of the rat α-fetoprotein originally present in the amniotic fluid.     

Clinical study on increased serum thyroxine-binding globulin in cancerous state

Serum thyroxine-binding globulin (TBG) in 169 patients with various cancers was determined by radioimmunoassay (RIA). Eleven patients showed a high serum TBG level (greater than 35 micrograms/ml). Two of them had been treated with estrogen for prostate cancer. One patient had high serum TBG with serum hepatitis. Another 8 cases had normal liver function and also normal levels serum estrogen. Thus, about 4.7% (8/169) of the cancer patients had high serum TBG and mild hyperthyroxinemia caused by unknown mechanisms. The high TBG level in these patients continued until just before death, or in some cases decreased to normal after removal of cancer tumors by operation. Cancer is occasionally associated with an increase in serum TBG. Although the mechanism is not clear, the increased TBG in the cancerous state in interesting and has significance as a tumor marker.     

Comprehensive proteomic analysis of human cervical-vaginal fluid

Cervical-vaginal fluid (CVF) is a potential rich source of biomarkers for enhancing our understanding of human parturition and pathologic conditions affecting pregnancy. In this study, we performed a comprehensive survey of the CVF proteome in pregnancy utilizing multidimensional liquid chromatography (2D-LC) coupled with mass spectrometry and gel-electrophoresis-based protein separation and identification. In total, 150 unique proteins were identified using multiple protein identification algorithms. Metabolism (32%) and immune response-related (22%) proteins are the major functional categories represented in the CVF proteome. A comparison of the CVF, serum, and amniotic fluid proteomes showed that 77 proteins are unique to CVF, while 56 and 17 CVF proteins also occur in serum and amniotic fluid, respectively. This data set provides a foundation for evaluation of these proteins as potential CVF biomarkers for noninvasive diagnosis of pregnancy-related disorders.     

Differences between newly formed and recycled free small ribosome subunits in liver cytoplasm.

1. Ferritin has been isolated from the serum of four patients with iron overload by using two methods. 2. In method A, the serum was adjusted to pH 4.8 and heated to 70 degrees C. After removal of denatured protein, ferritin was concentrated and further purified by ion-exchange chromatography and gel filtration. In most cases, only a partial purification was achieved. 3. In method B, ferritin was extracted from the serum with a column of immuno-adsorbent [anti-(human ferritin)] and released from the column with 3M-KSCN. Further purification was achieved by anion-exchange chromatography followed by the removal of remaining contaminating serum proteins by means of a second immunoadsorbent. Purifications of up to 31 000-fold were achieved, and the homogeneity of the final preparations was demonstrated by polyacrylamide-gel electrophoresis. 4. Serum ferritin purified by either method has the same elution volume as human spleen ferritin on gel filtration on Sephadex G-200. Serum ferritin has a relatively low iron content and iron/protein ratios of 0.023 and 0.067 (mug of Fe/mug of protein) were found in two pure preparations. On anion-exchange chromatography serum ferritin has a low affinity for the column when compared with various tissue ferritins. Isoelectric focusing has demonstrated the presence of a high proportion of isoferritins of relatively high pI. 5. Possible mechanisms for the release of ferritin into the circulation are briefly discussed.     

Estimation of the Stokes radii of serum proteins for a study of protein movement from blood to amniotic fluid.

The effective hydrodynamic (Stokes) radii of fifteen serum proteins were estimated by Sephadex G 200 gel filtration and immunochemical methods. The Waldmann-Meyer and Birch equation (Protides Biol. Fluids, Proc. 21st Colloq. (1974) (Peeters, H., ed.), Vol. 21, pp. 653-656, Pergamon Press, Oxford) was used for maximum accuracy. Three replicate column runs were made to assess the precision for the size determinations (coefficients of variation 0.6-2.7(). Quantive two-dimensional immunoelectrophoresis was used to measure eleven proteins in specimens of serum and amniotic fluid collected from twelve normal pregnancies. There was a close inverse linear relationship between the amniotic fluid/serum ratios of the proteins and their Stokes radii. This indicates that the movement of a protein from the blood to amniotic fluid is determined by the size of the protein. The linear correlation of protein amniotic fluid/serum ratio with Stokes radius was better than that with molecular weight. This demonstrates that, as an expression of protein size, Stokes radius should be used in preference to molecular weight when protein filtration systems are being investigated.     

THE NATURE AND ORIGIN OF THE SOLUBLE PROTEIN IN HUMAN AMNIOTIC FLUID

1. Amniotic fluid surrounds the human fetus and is separated from the uterus by the amnion, chorion and placenta. The ability to obtain samples of amniotic fluid from women by a simple procedure has encouraged studies on the nature and origin of the fluid, and on its use for the diagnosis of a variety of clinical conditions. The fluid contains cells, which are of fetal origin, and can be grown in a tissue culture. Cyto-genetic and biochemical analyses can therefore be used to detect chromosomal aberrations and inborn errors of metabolism in the fetus. 2. The supernatant of amniotic fluid contains many of the solutes typical of extracellular fluid. In particular, it contains a wide range of proteins and those which are of fetal origin are likely to be of use in the prenatal diagnosis of fetal disease. This review examines the nature and origin of the soluble protein in amniotic fluid, and discusses the diagnostic uses of the proteins which are of fetal origin. 3. In other mammals, the arrangement of the fetal membranes is different from that in man, and these differences are reflected by changes in the nature of the amniotic fluid. Thus data from other animals have little applicability to man. 4. Electrophoresis and immunoelectrophoresis have established that the major proteins in amniotic fluid are also present in maternal and fetal sera. Their concentrations in the fluid are influenced by their molecular weight and proteins larger than about 2.5 times 10⁶ may be excluded. Towards term, phenotyping studies show that a number of serum proteins in amniotic fluid are of maternal origin. In the case of group-specific component (Gc) this has been shown to be so throughout pregnancy. Such proteins must enter the fluid by diffusing across either the chorion or the chorionic plate and then the amnion. 5. It has been previously claimed that various serum proteins in amniotic fluid are of fetal origin. For albumin and IgG there are data that strongly support a maternal origin. The evidence on the origin of insulin is inconclusive. The concentration of β₂-microglobulin in amniotic fluid exceeds that in maternal serum and is probably too high also for fetal serum to be its major source. It has a wide tissue distribution and probably enters the fluid from surrounding structures. 6. Alpha-fetoprotein in amniotic fluid is of fetal origin as it is present in maternal serum at far lower concentrations. It is found in fetal serum, urine and yolk sac, but it is not clear how it enters the amniotic fluid of normal fetuses. The concentrations of Gc and alpha-fetoprotein have been measured in amniotic fluid and in their sera of origin. The relative concentration of Gc in amniotic fluid was found to be much greater than that of alpha-fetoprotein and the concentration gradients of these marker proteins can be compared with data for other proteins. In this way further evidence has been obtained that the albumin, α₁,-antitrypsin and transferrin in amniotic fluid are mainly of maternal origin throughout pregnancy. 7. Immunological studies have shown that at least three proteins of non-serum origin are present in amniotic fluid and they have also been located in the amnion and uterine decidua. 8. The enzymes present in amniotic fluid are summarized. Many lysosomal enzymes are clearly of fetal origin since they show altered specific activities in the appropriate cases where the fetus is affected with an inborn error of metabolism. For other enzymes, analysis of specific activity gradients can help to decide the extent to which an enzyme is of serum origin, although this will not exclude the possibility of a maternal (uterine) contribution. The results of such analyses suggest that, relative to the serum protein in amniotic fluid, the greatest concentrations of the minor non-serum proteins in the fluid occurs between thirteen and eighteen weeks of pregnancy and also towards term. 9. Some inborn errors of metabolism may be diagnosed prenatally by measuring the specific activity of the respective enzyme in amniotic fluid. However, the presence of different enzymes with similar substrate specificities has prevented this in Pompe's disease. 10. In cases where the fetus is affected with anencephaly or spina bifida there is an increase in the concentration of alpha-fetoprotein in the amniotic fluid. This has provided a way of detecting these diseases early enough to allow termination of pregnancy. 11. The discovery of new proteins in fetal serum and in the tissues surrounding the amniotic cavity would seem to provide the best chance of extending the uses of amniotic fluid into the other areas of prenatal medicine.