N-acetyl-D-galactosaminyltransferase in human serum and erythrocyte membranes

Complementary innate (anti-A-specific) IgM emerging from ontogenic O-GalNAc-transferase depletion: (Innate IgM complementarity residing in ancestral antigen completeness)

The murine and the human genome have global properties in common. So the murine anti-A-specific complementary IgM and related human innate isoagglutinin represent developmental, 2-mercaptoethanol-sensitive, complement-binding glycoproteins, which do not arise from any measurable environmentally-induced or auto- immune response. The murine anti-A certainly originates from a cell surface- or cell adhesion molecule, which in the course of germ cell development becomes devoid of O-GalNAc-transferase and is released into the circulation. In human sera the enzyme occurs exclusively in those of blood group A- and AB subjects, while in group O(H) an identically encoded protein lets expect an opposite function and appears in conjunction with a complementary anti-A reactive glycoprotein. Since O-glycosylations rule the carbohydrate metabolism in growth and reproduction processes, we propose that the ancestral histo-(blood)-group A molecule arises in the course of O-GalNAc-glycosylations of glycolipids and protein envelops at progenitor cell surfaces. Germ cell development postulates embryonic stem cell fidelity, which is characterised by persistent production of α-linked O-GalNAc-glycans. They are determined by the A-allele within the human, "complete" histo (blood) group AB(O) structure that in early ontogeny is hypothesised to be synthesised independently from the final phenotype. The structure either passes "completely" through the germline, in transferase-secreting mature tissues becoming the "complete" phenotype AB, or disappears in exhaustive glycotransferase depletion from the differentiating cell surfaces and leaves behind the "incomplete" blood group O-phenotype, which has released a transferase- and O-glycan-depleted, complementary glycoprotein (IgM) into the circulation. The process implies, that in humans the different blood phenotypes evolve from a "complete" AB(O) molecular complex in a distinct enzymatic and/or complement cascade suggesting O-glycanase involvements. While the murine and human oocyte zona pellucida express identical O-glycans, the human phenotype O might be explainable by the kinetics of the murine ovarian O-GalNAc glycan synthesis and the complementary anti-A released in parallel. The maturing murine ovary may provide insight into encoding of the physiologically superior α-linked GalNAc ancestral epitope that becomes essential in reproduction as well as in tissue renewal events. According to recent reports, O-GalNAc-transferase-determined blood group A suggests superiority in human female fertility and was called even "protective". So the minor fertility of blood-group-O females may reside in a critical timing in developmental shifting of enzyme functions affecting the formation of GalNAc-determined hormone receptors on the way to maturation. Experiments that had inserted an oocyte genome into a somatic one to generate pluripotent stem cells, might elucidate a developmental dilemma by testing oocytes from different blood group AB donors donors. Perhaps they will unmask the molecular basis of an evolutionary trend, while stem cell generation itself capitalises on the enzymatically-advantaged, lineage-maintaining (histo) blood group A-allele, which guaranties ancestral functional completeness.

Unravelling the biochemical basis of blood group ABO and Lewis antigenic specificity

The ABO blood-group polymorphism is still the most clinically important system in blood transfusion practice. The groups were discovered in 1900 and the genes at the ABO locus were cloned nearly a century later in 1990. To enable this goal to be reached intensive studies were carried out in the intervening years on the serology, genetics, inheritance and biochemistry of the antigens belonging to this system. This article describes biochemical genetic investigations on ABO and the related Lewis antigens starting from the time in the 1940s when serological and classical genetical studies had established the immunological basis and mode of inheritance of the antigens but practically nothing was known about their chemical structure. Essential steps were the definition of H as the product of a genetic system Hh independent of ABO, and the establishment of the precursor-product relationship of H to A and B antigens. Indirect methods gave first indications that the specificity of antigens resided in carbohydrate and revealed the immunodominant sugars in the antigenic structures. Subsequently chemical fragmentation procedures enabled the complete determinant structures to be established. Degradation experiments with glycosidases revealed how loss of one specificity by the removal of a single sugar unit exposed a new specificity and suggested that biosynthesis proceeded by a reversal of this process whereby the oligosaccharide structures were built up by the sequential addition of sugar units. Hence, the primary blood-group gene products were predicted to be glycosyltransferase enzymes that added the last sugar to complete the determinant structures. Identification of these enzymes gave new genetic markers and eventually purification of the blood-group A-gene encoded N-acetylgalactosaminyltransferase gave a probe for cloning the ABO locus. Blood-group ABO genotyping by DNA methods has now become a practical possibility.

Surface-associated glycosyltransferase activities in rat Sertoli cells in vitro

We have previously demonstrated fucosyltransferase (FT) activity on mouse germ cell surfaces at different stages of spermatogenesis. To complement these findings, here we report FT activity on the Sertoli cell (SC) surface. SC isolated and cultured from 20-day-old rat testes displayed FT activity with a Vmax of 12.5 pmoles/mg protein/min and a Km of 22 microM, while purified Sertoli cell plasma membranes (SCPM) showed FT activity with a Vmax of 10 pmoles/mg protein/min and a Km of 18.2 microM for GDP-[14C]-L-fucose. Fucosyltransferase activities were 16.7 and 2.6 pmoles/mg protein/min in SC and SCPM, respectively; approximately 16% of FT activity is, therefore, on the cell surface. To test whether the expression of FT activity in SC was regulated by hormones and growth factors, SC were cultured in serum-free medium supplemented with insulin, transferrin, sodium selenite, and epidermal growth factor (medium 4F) or in 4F plus follicle-stimulating hormone, testosterone, hydrocortisone, and vitamin E (medium 8F). We found that FT activity in SC is not modulated by these hormones or growth factors (4F or 8F). For comparison with FT, galactosyltransferase (GalTase) activities in SC and SCPM were also determined. SC displayed GalTase activity with a Vmax of 50 pmoles/mg protein/min and a Km of 38.5 microM, while SCPM showed GalTase activity with a Vmax of 25 pmoles/mg protein/min and a Km of 20.8 microM for UDP-[3H]-galactose. Galactosyl-transferase activities were 29.2 and 9.6 pmoles/mg protein/min in SC and SCPM, respectively. Therefore, approximately 33% of the total cell GalTase activity was detected on the surface membranes of rat Sertoli cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Fluorescence in situ hybridization for the Y-chromosome can be used to detect cells of recipient origin in allografted hearts following cardiac transplantation

The purpose of this study was to determine if fluorescence in situ hybridization for the Y-chromosome can be used to detect cells of recipient origin in allografted hearts following cardiac transplantation. Formalin-fixed, paraffin-embedded tissue sections of coronary arteries from two hearts surgically explanted from heart transplant recipients undergoing retransplantation because of accelerated arteriosclerosis were examined by fluorescence in situ hybridization for the presence of cells containing the Y-chromosome using a biotinylated Y-chromosome cocktail probe. In both cases, the recipients were male and the original donor hearts were obtained from female donors. Hybridization was detected in cells morphologically recognizable as infiltrating lymphocytes, macrophages, and mast cells, establishing that these cells in the donor hearts were of recipient origin. In contrast, hybridization was not detected in cardiac myocytes, in vascular smooth muscle cells, or in the majority (>95%) of endothelial cells, suggesting that these cells were of donor origin. Although hybridization was detected in rare flattened cells lining vascular lumina, these cells did not stain for factor VIII, suggesting that they were, in fact, flattened inflammatory cells and not endothelial cells. These results demonstrate that, when the recipient and donor are of the opposite sex, fluorescence in situ hybridization for the Y-chromosome can be used to detect graft chimerism in transplanted hearts.

Detection and activity of blood group B gene-associated alpha-galactosyltransferase in human urine

alpha-Galactosyltransferase which participates in the biosynthesis of blood group B substance was found in urine from group B and AB healthy persons of both secretors and non-secretors. The activity of alpha-galactosyltransferase in the urine of a healthy variant Bm person was lower than that found in a normal group B person. This enzyme in urine of A1Bm persons must be much lower than that in normal AB persons. Its activity was not detected by the method of group O to group B transformation or erythrocytes.

alpha-N-acetyl-D-galactosaminyl- and alpha-D-galactosyltransferase activities in sera of cis AB blood group individuals

Thirteen cis AB persons from five families were examined for serum glycosyltransferase activities associated with the biosynthesis of A and B blood group characters. Their transferases were generally homogeneous within one family, except for A2/cis AB genotypes, whose A enzyme level was similar to the A2 normal sera, but they varied from one family to another. These activities differed quantitatively and qualitatively from A, B and AB normal sera. Studies of A transferase showed variations in the pH-dependent curve, the effect of cofactors and the capacity of conversion of O red cells into A-active cells. Moreover, A and B transferases behaved differently with respect to their relative levels than did AB heterozygous normal sera. The results were discussed and it was suggested that a mutation of a single enzyme transferring both galactose and N-acetyl-galactosamine could explain these properties.

Human blood-group A- and H-specified glycosyltransferase levels in the sera of newborn infants and their mothers

The level of blood-group A1-specified alpha,3'-N-acetyl-D-galactosaminyl-transferase in the serum of recently-delivered women was found to be appreciably lower than the level of this enzyme in the serum of non-pregnant adults and of newborn infants; a similar but less striking decrease was observed in the levels of the A2-specified alpha,3'-N-acetyl-D-galactosaminyltransferase and the H-specified alpha,2'-L-fucosyltransferase. Although the red cells of newborn infants are known to have relatively few A and H antigen sites, the serum of neonates was found to have a level of A1- and A2-dependent N-acetylgalactosaminyltransferases and H-dependent fucosyltransferase as high as, if not higher than, the serum of non-pregnant adults. This finding is compatible with the fact that the haemopoietic tissue contributes only about 20% of the serum transferase level.

Human plasma uridine diphosphate galactose-glycoprotein galactosyltransfertase. Purification, properties and kinetics of the enzyme-catalysed reaction

The soluble galactosyltransferase of human plasma catalysed the transfer of galactose from UDP-galactose to high- and low-molecular-weight derivatives of N-acetylglucosamine, forming a beta-1-4 linkage. The enzyme was purified by using (NH4)2SO4 precipitation and affinity chromatography on an alpha-lactalbumin-Sepharose column. The galactosyltransferase was maximally bound to this column in the presence of N-acetylglucosamine, and the enzyme was eluted by omitting the amino sugar from the developing buffer. The molecular weight of the enzyme was estimated to be 85000 by gel filtration. The assay conditions for optimum enzymic activity was 30 degrees C and pH7.5. Mn2+ ion was found to be an absolute requirement for transferase activity. The Km for Mn2+ was 0.4 mM and that for the substrate, UDP-galactose, was 0.024 mM. The Km for the acceptors was 0.21 mM for alpha1-acid glycoprotein and 3.9 mM for N-acetylglucosamine. In the presence of alpha-lactalbumin, glucose became a good acceptor for the enzyme and had a Km value of 2.9 mM. Results of the kinetic study indicated that the free enzyme reacts with Mn2+ under conditions of thermodynamic equilibrium, and the other substrates are added sequentially.

Enzymatic conversion of human group O red cells into Group B active cells by alpha-D-galactosyltransferases of sera and salivas from group B and its variant types

Salivas from group B secretor or non-secretor, acting on O red cells in the presence of UDP-galactose, each converted them into B cells, which were agglutinated against anti-B human serum (1:512) at the titre of thirty-two-fold, while secretor or non-secretor group AB salivas converted O red cells into B active cells, which were agglutinated by anti-B human serum (1:512) at the titre of eight- to sixteen-fold. The results indicate that the alpha-galactosyltransferases which participate in the biosynthesis of group B substance are secreted in group B or AB salivas of both secretor and non-secretor types as well as in their sera. Agglutinabilities of enzymatically converted B-active red cells against anti-B human serum indicate that alpha-galactosyltransferase activities of both serum and saliva from a weak B (Bw) individual, who has weak B antigens in red cells and saliva, were lower than those of normal group B. The alpha-galactosyltransferase activities in group Bm sera were lower than those of normal group B, while the enzyme activities in salivas of group Bm were demonstrated to the same degree in normal group B salivas.

Cancer-associated isoenzyme of serum galactosyltransferase

Galactosyltransferase activity was assayed in sera from 58 patients with various types of cancer. On discontinuous polyacrylamide gel electrophoresis a slow-moving peak of galactosyltransferase activity (isoenzyme II) was found to be present in the serum of 43 of these patients in addition to the major isoenzyme I. Isoenzyme II was found in only 2 of 39 patients with various nonmalignant disorders and was not detected in the serum of 22 normal control subjects. There was no correlation between the presence of this electrophoretically distinct isoenzyme and total serum galactosyltransferase activity, alkaline phosphatase, levels of carcinoembryonic antigen, or blood type. However, patients with widespread metastases had significantly higher isoenzyme II levels than those with no metastases or with limited local spread. Further studies will be necessary to evaluate the clinical usefulness of this serum galactosyltransferase isoenzyme in the diagnosis and monitoring of patients with neoplastic disease.

Activity of B-gene-specified galactosyltransferase in individuals with Bm phenotypes

Blood group B-gene-specified alpha-galactosyltransferase was determined in serums and erythrocyte membranes of several related persons with Bm phenotypes. The level of this enzyme in serums was similar to, but in erythrocyte membranes much lower than that found in normal B and AB persons.

The action of group Bm or CisAB sera on group O red cells in the presence of UDP-D-galactose

Group B and AB sera, acting on O red cells in the presence of UDP-galactose, each converted them into B active cells, which were agglutinated by anti-B human serum (1:512) at the titer of 128-fold, while group Bm and A-1 Bm sera, converted O red cells similarly incubated into B active cells, which were agglutinated by anti-B human serum (1:512) at the titer of 8- to 16-fold. This indicates that alpha-galactosyltransferase activity in Bm and A-1 Bm sera may be about 1/8-1/16 that in B and AB sera. Group CisAB sera, even after absorption of cold anti-B agglutinins with packed, washed group B red cells, did not convert O red cells in the presence of UDP-galactose in such a way that they might agglutinate against anti-B human serum.

Alterations of membrane glycopeptides in human colonic adenocarcinoma

Membrane glycopeptides were examined in human colonic adenocarcinoma and normal colonic mucosa. The carbohydrates of membrane glycopeptides were found to be markedly reduced in tumor tissue and the relative proportions of the various sugars were altered. Although all of the sugars were lower in tumor tissue when compared to the adjacent normal mucosa, galactosamine, fucose, and sialic acid were more significantly reduced. Examination of the blood group activity and lectin-binding properties of membrane glycopeptides revealed that specific carbohydrate structures had changed in the tumor tissue. Most striking of these changes was the disappearance of glycoprotein-associated blood group A activity. Assay of the enzyme responsible for synthesis of the blood group A determinant showed that this glycosyltransferase activity was greatly diminished in tumor tissue. A galactosyltransferase and a fucosyltransferase were also significantly lower in the tumor tissue whereas the levels of another galactosyltransferase and a sialyltransferase were unaltered. Glycosidase activities in the normal and tumor tissues were similar. The results show that an alteration in glycoprotein biosynthesis occurred during tumorigenesis that resulted in a modified membrane glycoprotein composition and that these changes are probably a reflection of reduced levels of the enzymes responsible for glycoprotein synthesis.

Qualitative differences in the N-acetyl-D-galactosaminyltransferases produced by human A1 and A2 genes

This study describes the kinetic properties of N-acetyl-D-galactosaminyltransferase in serum from subjects with blood groups A(1) and A(2). When the A(1) and A(2) enzymes were compared, with lacto-N-fucopentaose I and 2'-fucosyllactose as acceptors, the enzymes differed in their cation requirements, pH optima, and K(m) values. The two acceptors competed for the same transferase. Mixing experiments showed that the lower activity of the A(2) enzyme could not be attributed to a modifier or inhibitor in serum. It was concluded that the A(1) and A(2) enzymes differ qualitatively.

Glycosyltransferases in human blood.I. Galactosyltransferase in human serum and erythrocyte membranes

Human serum and hemoglobin-free erythrocyte membranes were found to contain a galactosyltransferase which catalyzes the transfer of galactose from UDP-galactose to specific large and small molecular weight acceptors. The requirements for enzyme activity were found to be similar for the enzymes from both sources. However, the membrane-bound enzyme depended on a detergent for maximal activity. Mn(++) was an absolute requirement for transfer and uridine nucleoside phosphates were inhibitors. The most effective acceptor for galactose was a glycoprotein containing N-acetylglucosamine residues in the terminal position of its oligosaccharide side chains, N-acetylglucosamine was also an acceptor. While the presence of alpha-lactalbumin in the incubation medium resulted in a significant decrease in the transfer of galactose to N-acetylglucosamine, glucose, which was not an acceptor for galactose in the absence of alpha-lactalbumin, became an excellent acceptor. The serum enzyme catalyzed the transfer of 54 nmoles of galactose per milliliter of serum per hour and its apparent K(m) for UDP-galactose was 7.5 x 10(-6)M. The membrane enzyme had a similar apparent K(m). Using a quantitative assay system the enzyme was found to be present in all individuals studied, regardless of their blood type, secretor status, or sex.

Glycosyltransferases in human blood. II. Study of serum galactosyltransferase and N-acetylgalactosaminyltransferase in patients with liver diseases

Serum galactosyltransferase activity was found to be elevated in patients with alcoholic and other liver disorders but remained at a normal level in patients with a variety of nonhepatic diseases. The properties of the galactosyltransferase in patients with liver disease were compared with those of the enzyme in the serum of normal subjects. The possible presence of inhibitors or activators in the serum was examined. Results indicated that in patients with liver disease, the rise in the serum galactosyltransferase was due to an increase in the level of the enzyme present in normal serum and not due to the appearance of a new enzyme. In the cases examined, the level of the enzyme increased with the deterioration of liver function and declined in a patient recovering from acute alcoholic hepatitis. Another glycosyltransferase, an N-acetylgalactosaminyltransferase, was not elevated in the serum of liver disease patients and, unlike the galactosyltransferase, was not detected in normal liver. The results suggest that the serum galactosyltransferase originates from the liver and that an abnormal rise in the level of this enzyme in serum is due to hepatocellular damage.

Glycoprotein biosynthesis in small intestine. 3. Enzymatic basis for the difference in the antigenicity of mucins

Rat small intestinal mucosa was examined for ability to produce mucins with human blood group A, B, and H activity. Blood group activity of the mucins was compared to antigenic activity of red blood cells in individual rats and the enzymatic basis for differences was investigated. Red cells in all the rats examined contained human blood group A and B antigens. All rats synthesized intestinal mucins having B and H antigenic activity but 57% failed to produce mucins with blood group A activity (A(-)); the remaining 43% (A(+)) produced A substance. The activities of five glycosyltransferases including alpha(1-->2) fucosyltransferase, the determinant of human secretor status, were measured in the intestine of A(+) and A(-) rats. Four enzymes were the same in both groups, while the fifth, N-acetylgalactosaminyltransferase, was present only in A(+) rats. The specificity of this latter enzyme, as found in the rat, appeared similar to that in humans, since it catalyzed addition of N-acetyl-D-galactosamine only to acceptors which had the H determinant structure. In the presence of the enzyme, A(-) mucin could be converted to A(+) mucin; this was shown both by hemagglutination inhibition and immunoprecipitin studies of the products of incubation of A(-) mucin with UDP-N-acetyl-D-galactosamine and the enzyme. These studies indicate that the difference between A(+) and A(-) rats is due to the apparent absence of N-acetylgalactosaminyltransferase in the intestinal mucosa of A(-) rats. These rats may provide experimental models for studies on the effect of ABO and secretor status on susceptibility to ulceration and carcinogenesis.