Carbohydrate structure of the concanavalin A molecular variants of alpha-fetoprotein

Diagnosing and monitoring hepatocellular carcinoma with alpha-fetoprotein: new aspects and applications

Hepatocellular carcinoma is the 5th most common cancer in the world. Prognosis for this disease is poor since hepatocellular carcinoma is mostly diagnosed at an advanced stage. Serum alpha-fetoprotein (AFP) is one of the most common diagnostic markers for hepatocellular carcinoma. However, its diagnostic value is more and more questioned. Therefore, research has focussed on AFP related parameters (AFP mRNA and AFP glycoforms). The aim of this paper is to review the present knowledge on AFP and its related parameters in diagnosing and monitoring HCC. AFP related parameters can be arranged in two types: AFP mRNA and AFP glycoforms. AFP mRNA is a potentially prognostic marker and AFP mRNA assays are based on PCR techniques. The AFP glycoforms have diagnostic potential and assays are based on isoelectric focussing and lectin affinity electrophoretic methods. Up to now the diagnostic use of the AFP related parameters is limited. Although some of them are recommended as a complementary test, they cannot (yet) replace serum AFP as the golden standard of diagnostic markers for hepatocellular carcinoma.

Serum N-acetylglucosaminyltransferase III activities in hepatocellular carcinoma

N-Acetylglucosaminyltransferase III (GnT III) catalyses the addition of N-acetylglucosamine through a beta 1-4 linkage to the mannose of the trimannosyl core, resulting in conversion of the concanavalin A (Con A)-reactive glycan into a non-reactive state. In this study, we measured GnT III activity to evaluate its diagnostic efficacy and its therapeutic effect on hepatocellular carcinoma (HCC). Concanavalin A-non-reactive fraction of serum transferrin (Tf) was also determined since the sugar chains of Tf are one of the possible candidates for the product of GnT III. Serum samples (159) were used from patients with HCC (89), liver cirrhosis (30), chronic hepatitis (19), alpha-fetoprotein (AFP) producing gastric carcinoma metastatic to the liver (five) and healthy controls (16). N-Acetylglucosaminyltransferase III activity was determined by high performance liquid chromatography. The reactivity of serum Tf to Con A was also analysed in 21 paired HCC samples before and after treatment by crossed immuno-affinoelectrophoresis. N-Acetylglucosaminyltransferase III activity from the HCC group (153 +/- 72pmol/mL/h) was significantly higher than that from liver cirrhosis (99 +/- 67 pmol/mL per h), chronic hepatitis (84 +/- 39 pmol/mL per h) and the normal controls (62 +/- 16 pmol/mL per h). N-Acetylglucosaminyltransferase III activity of 21 patients with HCC was significantly reduced after treatment such as transcatheter arterial chemoembolization and/or percutaneous ethanol infection therapy, (123 +/- 77 to 100 +/- 60 pmol/mL per h). Commensurate decreases of AFP and des-gamma-carboxy prothrombin with GnT III activity were also observed after treatment. The Con A-non-reactive fraction (n = 21; 6.4 +/- 2.3%) in patients with HCC after treatment was significantly lower than before (8.2 +/- 2.4%). The present study suggests that GnT III activity is a possible aid in the diagnosis and evaluation of HCC, especially when other tumour markers are negative.

Diagnosis of hepatocellular carcinoma by concanavalin A affinity electrophoresis of serum alpha-fetoprotein

BACKGROUND

Concanavalin A (Con A) affinity electrophoresis of serum alpha-fetoprotein (AFP) can distinguish hepatocellular carcinoma (HCC) from other malignancies when the serum AFP concentration is elevated. However, Con A has not been able to distinguish HCC from benign chronic liver disease such as cirrhosis or chronic hepatitis.

METHODS

The Con A affinity electrophoresis of serum AFP was analyzed in patients with a serum AFP concentration greater than 50 ng/mL by antibody affinity electrophoresis and Western blotting in an attempt to distinguish hepatocellular carcinoma from benign chronic liver disease. Before the assay, the serum AFP concentrations were adjusted between 100 ng/ml and 300 ng/ml by concentrating or diluting the samples.

RESULTS

Of 180 patients with HCC, 44 (24%) had a single band and 91 (51%), 35 (19%), and 10 (6%) had 2, 3, and 4 bands, respectively. All 35 patients with chronic hepatitis had a single band. All but 1 of 72 patients with cirrhosis had a single band. Multiple AFP bands on Con A affinity electrophoresis appear to be diagnostic of HCC. This method has a sensitivity of 76%, a specificity of 99%, a positive predictive value of 99%, and a negative predictive value of 71% for detecting HCC. The number of AFP bands correlated with serum AFP concentration and tumor size in patients with HCC.

CONCLUSIONS

This assay is useful for distinguishing HCC from benign chronic liver diseases.

Germ cell tumors express a specific alpha-fetoprotein variant detectable by isoelectric focusing

BACKGROUND

Many nonseminomatous germ cell tumors (NSGCTs) express elevated levels of serum alpha-fetoprotein (AFP), which is widely used for diagnosis and monitoring therapy. Alpha-fetoprotein is also expressed in patients with hepatocellular carcinoma (HCC). In these sera, several variants, some highly specific, recently have been detected by isoelectric focusing.

METHODS

Sera were collected from nine patients with NSGCTs, five pregnant women, and five patients with HCC. After isoelectric focusing, the proteins were transferred to nitrocellulose membrane by blotting and incubated with polyclonal rabbit antihuman AFP conjugated with horseradish peroxidase. The enhanced chemiluminescence detection system and Hyperfilm-ECL were used to render the protein bands visible and each was quantified as a percentage of the total AFP using a densitometer.

RESULTS

Isoelectric focusing of serum alpha-fetoprotein from the patients with NSGCTs (four testicular, five mediastinal) revealed a consistent pattern characterized by a specific band (band +III). A second band (band +II) that is also seen in sera from patients with hepatocellular carcinoma was present in all patients. The overall pattern was distinct from that of AFP from HCC and that produced during late pregnancy. The two characteristic bands (AFP +II and +III) were responsible for the great majority of total AFP in these patients; estimation of serial sera in patients undergoing treatment showed that total and "malignant" AFP changed in parallel. Banding patterns, apart from one patient, were identical in patients with testicular and mediastinal NSGCTs.

CONCLUSION

NSGCTs tumors express a highly consistent and specific pattern of AFP variants. More detailed analysis of AFP patterns in larger numbers of patients may provide further insight into the cellular heterogeneity of germ cell tumors.

Alteration of asparagine-linked glycosylation in serum transferrin of patients with hepatocellular carcinoma

The asparagine-linked sugar chains in serum transferrin purified from patients with hepatocellular carcinoma (n = 13), healthy individuals (n = 5) and patients with liver cirrhosis (n = 6) were compared. Sugar chains released with N-glycanase from desialylated and pepsin-digested transferrin were derivatized by reductive pyridylamination. Analysis of the sugar chains by high performance liquid chromatography in combination with exoglycosidase digestion revealed an increase of a biantennary complex-type sugar chain with a fucosylated trimannosyl core; Gal beta 1-4GlcNAc beta 1-2Man alpha 1-6(Gal beta 1-4GlcNAc beta 1-2Man alpha 1-3) Man beta 1-4GlcNAc beta 1-4(Fuc alpha 1-6)GlcNAc in 7 of 13 cancer patients and an increase of a sugar chain with a fucosylated trimannosyl core and bisecting N-acetylglucosamine; Gal beta 1-4GlcNAc beta 1-2Man alpha 1-6(GlcNAc beta 1-4) (Gal beta 1-4GlcNAc beta 1-2Man alpha 1-3)Man beta 1-4GlcNAc beta 1-4(Fuc alpha 1-6)GlcNAc in one of the 13 cancer patients. Further, the fucosylated alteration of the sugar chain was detected also in alpha 1-antitrypsin, hemopexin, alpha 1-acid glycoprotein and alpha 2-HS glycoprotein from one of the patients with increased fucosylated transferrin.

Fucosylation index of alpha-fetoprotein, a possible aid in the early recognition of hepatocellular carcinoma in patients with cirrhosis

We report here on three patients with cirrhosis for whom an early recognition of hepatocellular carcinoma was made possible by the measurement of the degree of fucosylation (fucosylation index) of alpha-fetoprotein. Increased levels of this index associated with a moderate increment of serum concentration of alpha-fetoprotein were observed in three patients with cirrhosis who showed no indication of hepatocellular carcinoma by several imaging modalities. Four years after the onset of an increase in the fucosylation index, small hepatocellular carcinoma with a tumor diameter less than 2 cm was revealed in case 1. In cases 2 and 3, small hepatocellular carcinomas were detected 24 mo and 9 mo, respectively, after the first sign of the increase in the index. However, the development to hepatocellular carcinoma was not detected in five patients with cirrhosis in whom continuous increments of serum concentration of alpha-fetoprotein with low levels of fucosylation index were observed during the prospective follow-up from 3 to 9 yr. These findings indicated that the fucosylation index of alpha-fetoprotein can be used as an aid in an early recognition of hepatocellular carcinoma, especially in patients with cirrhosis during the follow-up process in which the moderate increment of serum concentration of alpha-fetoprotein is noted.

The usefulness of simultaneous determinations of glucosaminylation and fucosylation indices of alpha-fetoprotein in the differential diagnosis of neoplastic diseases of the liver

The degrees of glucosaminylation (glucosaminylation index) and fucosylation (fucosylation index) of alpha-fetoprotein (AFP) were determined in serum samples of 351 patients with hepatocellular carcinoma (HCC), 47 with carcinoma metastatic to the liver from digestive organs, five with mixed cholangiocellular and HCC, and 176 with benign liver diseases. The glucosaminylation index of AFP in patients with carcinoma metastatic to the liver (42 +/- 23%, mean +/- SD) was significantly higher than that in patients with HCC (5 +/- 7%, P less than 0.001) or that in patients with benign liver diseases (2 +/- 4%, P less than 0.001). The fucosylation indices of AFP in patients with carcinoma metastatic to the liver, with HCC, and with benign liver diseases were 76 +/- 25%, 42 +/- 30%, and 4 +/- 6%, respectively. Thus, the fucosylation indices of AFP were high in two neoplastic liver diseases (carcinoma metastatic to the liver and HCC) and low in benign liver diseases, whereas the glucosaminylation indices were high in carcinoma metastatic to the liver but low in HCC and benign liver diseases. When the values of 30% and 80% were used as the level of the glucosaminylation and fucosylation indices, respectively, to discriminate carcinoma metastatic to the liver from HCC, 40 of 47 patients with carcinoma metastatic to the liver (85%) were able to be discriminated from HCC (sensitivity). The specificity, the positive predictive value, and the overall accuracy were 86% (302/351), 45% (40/40 + 47 + 3 - 2) and 86% (40 + 302/47 + 351), respectively. These data suggest that the combined information in these two indices provides a potent criterion for the diagnosis of neoplastic diseases of the liver.

Chemistry and biology of alpha-fetoprotein

Alpha-Fetoprotein (AFP) is a product of specific fetal tissues and of neoplastic cells of hepatocyte or germ cell origin in adults. This protein belongs to a gene family that is phylogenetically most closely related to serum albumin. Its primary, secondary, and tertiary structural aspects appear similar to the three-domain concept proposed for the latter protein. The primary sequence of AFP departs most widely from serum albumin in the first 135 amino acid residues, with about 42% of the remaining 590 residues of the human proteins being identical. Some evidence exists that there are limited sequence differences in the AFP of a given animal species. AFP shows considerable charge heterogeneity that appears to relate mostly to its glycoid moiety. The proteins of some species such as the rat show more pronounced heterogeneities than that of humans. The variations in extent and type of glycosylations are evidenced by differences in the binding to various lectins. These interactions are being extensively explored in attempts to differentiate the sources of the protein produced by various normal and neoplastic cells and may provide valuable diagnostic methods. AFP, like serum albumin, shows relatively strong binding affinities for a variety of ligands. The most notable difference is the strong preferential binding of polyunsaturated fatty acids by AFP. This protein may play a role in transporting these substances to developing and to malignant cells. Various agents affect the synthesis of this protein both by specific fetal tissues and by neoplastic cells. Marked differences in the responses of cells, particularly those of neoplastic types, are indicative of variations in the genetic factors responsible for control of its synthesis. The subject of the genomic repression of the synthesis of AFP seen in fetal life upon maturation of the liver and the reoccurrence of synthesis upon malignant conversion of hepatocytes and of certain germ cells are of particular interest. The regulation of the closely related AFP and albumin genes is providing a powerful and attractive model to examine molecular events in the activation and inactivation of specific genes during development and in oncogenic processes. Extensive measurements of AFP during pregnancy and in the course of neoplasias, notably hepatoma, are being made to aid in following changes in such developments. Various specific physiological roles for this protein are also being proposed. One of these is its possible action in the regulation of immune processes.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of cross-reactivity of alpha-fetoprotein monoclonal antibody on quantitation of serum AFP and radioimmunodetection of hepatocellular carcinoma

Murine hybridomas were generated by immunizing mice with purified alpha-fetoprotein (AFP) to determine the cross-reactivity of AFP antibodies with human serum albumin (HSA). Eighteen out of 23 hybridoma products were cross-reactive with HSA. All 23 monoclonal antibodies (MAbs) could be subgrouped into 3 groups by their binding affinity to AFP and HSA, and one MAb from each group, IIB3, IIIB1 and IIIC6, were chosen for this study. The affinity to AFP was highest for IIB3 followed by IIIC6 and IIIB1, and that to HSA was in the order IIIB1 greater than IIB3. Immunohistochemical staining revealed no cross-reactions of these antibodies with HSA at the tissue level. IIB3 was the most efficient in the quantitative assays, indicating high affinity and specificity (non-cross-reactivity) of the antibodies, both of which are prerequisites for in vitro assays. Scans with good tumor localization were obtained from mice which received 131I-labeled IIB3 or IIIC6 after xenografting of the human hepatocellular carcinoma. The images obtained with IIB3 were inhibited in the presence of either AFP or HSA in the circulation. These findings indicated that the use of cross-reactive and/or high-affinity antibodies against AFP provides an inhibitory factor for tumor localization. MAb IIIC6, because of its high specificity and moderate affinity to AFP, seems to be the best candidate for immunoscintigraphy of the tumors in future studies.

A lectin-immunofluorometric assay using an immobilized Bandeiraea simplicifolia II lectin for the determination of galactosylation variants of glycoproteins

The sandwich-type immunometric assay was modified by replacing the solid phase-bound antibody with a lectin for the determination of glycoproteins carrying terminal N-acetylglucosamine residues. Microwells were coated with Bandeiraea simplicifolia II lectin and incubated with glycosylation variants of human serum glycoproteins. The bound glycoproteins were detected by time-resolved fluorometry using europium-labeled antibodies. Agalacto-derivatives of alpha 1-acid glycoprotein and transferrin obtained by neuraminidase and beta-galactosidase treatment bound to the immobilized lectin, whereas the native or desialylated glycoproteins showed no binding. The measuring range of the method for agalacto-alpha 1-acid glycoprotein was 0.01 to 10 micrograms/ml and for agalacto-transferrin 1 to 300 micrograms/ml. The binding of the agalacto-glycoproteins was totally inhibited with 1 to 10 mM N-acetylglucosamine which confirmed the specificity of the method for glycoproteins containing terminal N-acetylglucosamine residues. The results indicate that the novel lectin-immunofluorometric method is sensitive and has a wide measuring range for the determination of glycosylation variants of glycoproteins.

Alpha-fetoprotein antibody-lectin enzyme immunoassay to characterize sugar chains for the study of liver diseases

An antibody-lectin enzyme immunoassay (EIA) technique was developed for the analysis of sugar chains of serum alpha-fetoprotein in various liver diseases. The anti-'alpha-fetoprotein'-IgG was coated on a microtiter plate and then treated with periodic acid. A serum sample was added to the plate and then a 'peroxidase'-conjugated lectin was added. The amount of lectin bound to the sugar chain of the 'alpha-fetoprotein' was estimated from the 'peroxidase' activity. The 'peroxidase' activities of 4 different lectins, LCA, Con A, LCA and EPHA, were compared. The LCA/'wheat germ agglutinin' activity ratio and LCA/EPHA activity ratio were increased in liver diseases and LCA/'wheat germ agglutinin' ratio showed a statistically significant difference between the chronic hepatitis and the liver cirrhosis groups (p less than 0.05). Furthermore, when serum samples were pretreated with sialidase, a statistically significant difference was observed in the LCA/EPHA and LCA/Con A ratios between the chronic hepatitis and the hepatoma groups (p less than 0.05). These results indicated that low sialylation at the non-reduced end of the sugar chains of 'alpha-fetoprotein' occurs in liver cirrhosis and that high fucosylation at the reduced end of N-acetylglucosamine residue of 'alpha-fetoprotein' occurs in hepatomas.

Studies on alpha-fetoprotein produced by renal cell carcinoma

A 58-year-old man was found to have a Stage IV primary renal cell carcinoma (RCC) invading the colon and producing alpha-fetoprotein (AFP). The preoperative serum AFP level of 418 ng/ml had decreased to the normal level of 0.9 ng/ml 3 weeks after the radical operation. As the high serum AFP level in RCC without metastasis to the liver is a rare condition, histopathologic studies were performed on surgical specimens. Histologically, the tumor was clear cell adenocarcinoma and AFP was detected in tumor cells immunohistochemically. A Concanavalin A (Con A) sepharose affinity chromatogram was performed to detect the component of AFP in this case. The Con A nonreactive fraction rate was as high as 47%, which indicated that the AFP of this RCC was of fetal type.

The fucosylation index of alpha-fetoprotein and its usefulness in the early diagnosis of hepatocellular carcinoma

The serum concentration and degree of fucosylation (fucosylation index) of alpha-fetoprotein (AFP) were determined in serum samples from 258 patients with hepatocellular carcinoma (HCC) and 114 patients with benign liver diseases. When the serum AFP concentration was below 1000 ng/ml, it could not be used as a measure to distinguish between HCC and benign liver diseases. However, the fucosylation index of AFP proved useful for such a purpose. The sensitivity of the analysis using the fucosylation index in total patients with HCC was 69%; the specificity was 96% in benign liver diseases, and the accuracy of this test was 77%. When HCC patients who were grouped according to tumor size (5 cm, 3 cm, and 2 cm in diameter) were analyzed, they all had a fucosylation index significantly higher than that in benign liver disease patients. The mean fucosylation index in 28 patients with a serum AFP concentration below 1000 ng/ml and a tumor diameter less than 3 cm was 26 +/- 30%. Corresponding values for 16 patients with an AFP concentration below 400 ng/ml and a tumor size less than 3 cm and for 8 patients with a concentration below 400 ng/ml and a tumor size less than 2 cm were 32 +/- 31% and 27 +/- 27%, respectively. These values were higher, with statistical significance, than those in patients with benign liver diseases. These data indicate that the measurement of the fucosylation index of AFP is useful for the early diagnosis of HCC.

Functional domains of the T lymphocyte plasma membrane: characterization of the polypeptide composition

Highly purified plasma membranes from calf thymocytes were fractionated by affinity chromatography on Concanavalin A-Sepharose into two subfractions, one eluting freely from the affinity column (MF1) and a second being specifically retained (MF2). SDS-polyacrylamide-gel-electrophoresis revealed different polypeptide patterns of the two plasma membrane subfractions. Polypeptides of apparent molecular weights of 170, 150, 110, 94, 39, and 30 kDa were several-fold enriched in the adherent fraction, MF2. In contrast, several proteins in the 55-65 kDa range were preferentially recovered in the non-adherent fraction. Five Five of the six polypeptides, preferentially recovered in MF2 proved to be glycoproteins, the 39 kDa peptide was non-glycosilated. The differences in the amounts of the polypeptides specifically enriched in the adherent fraction MF2 became even more clear-cut when plasma membranes solubilized with non-ionic detergents (lysolecithin, ET-18-2H, Triton-X-100) were separated by affinity chromatography on Concanavalin A-Sepharose. The non-glycosilated peptide of apparent molecular weight of 39 kDa was recovered together with several glycoproteins in the adherent fraction, MF2, suggesting that not single glycoproteins, but plasma membrane domains were separated by Concanavalin A-Sepharose. Although the glycoproteins of the non-adherent fraction MF1 bound significant amounts of Concanavalin A, the major Concanavalin A binding glycoproteins were recovered in the adherent fraction, MF2. The plasma membrane subfractions showed also different functional properties, the specific activities [Na+ + K+]AT-Pase, Ca2+ ATPase and lysolecithin acyltransferase were several-fold enriched in the adherent fraction, MF2, as compared to MF1. The data suggest the existence of plasma membrane domains in the plasma membranes of thymocytes consisting of a different set of proteins, among others the major Concanavalin A binding glycoproteins with some membrane bound enzymes, probably implicated in the initiation of lymphocyte activation.

New placental proteins: chemistry, physiology and clinical use

In the past decade, several new placental proteins have been isolated and studied. The 'pregnancy-specific' beta 1-glycoprotein (SP1) is a major placental product with unusual physicochemical properties that has been extensively investigated, but its biological function remains uncertain. Pregnancy-associated plasma protein A (PAPP-A), a glycoprotein of mol. wt 400,000, has effects in vitro on the coagulation and complement cascades, probably by its properties of protease inhibition. Placental protein 5 (PP5) may be involved in the coagulation and fibrinolytic systems, and in follicle maturation and semen liquefaction. 'Placental protein 12' (PP12) is not a product of the placenta at all; it appears to be produced in the female genital tract under the influence of progesterone and may also be produced by proliferating liver cells. Further study may reveal new roles for these placental proteins beyond their traditional roles as tumour markers.

Fucosylation of serum alpha-fetoprotein in patients with primary hepatocellular carcinoma

alpha-Fetoprotein specimens were prepared from the sera of four patients with hepatocellular carcinoma. The lentil lectin-reactive and lectin-nonreactive variants of this glycoprotein were also prepared from the serum of one of the four patients by affinity chromatography with immobilized lectin. The correlation between the carbohydrate structure of these compounds and their reactivity in crossed immuno-affinoelectrophoresis with lentil lectin was studied by chemical analysis and affinity chromatography of the glycopeptides with lectin columns. It was found that the lentil lectin-reactive variant contained a carbohydrate chain of the fucosylated biantennary complex type. These data together with previous findings indicate that most of the patients with hepatocellular carcinoma have an elevated serum concentration of fucosylated alpha-fetoprotein.

Differences in the structure of alpha-fetoprotein and its clinical use in pediatric surgery

Techniques have been studied which distinguish two variants of human alpha-fetoprotein (AFP) on the basis of characteristics of the carbohydrate moiety of this glycoprotein. AFP in serum samples from six children with tumors of yolk sac origin showed little concanavalin-A (Con A) binding. In contrast, Con A binding of AFP was almost complete in serum samples from 14 other subjects with elevated AFP, including two with liver-cell tumors, eight with neonatal cholestasis, and four normal newborn infants. Differences were confirmed by immunoelectrophoretic studies. Thus, AFP from cells of yolk sac origin can be distinguished from AFP from liver cells or from tumors of hepatic cell origin.

Evaluation of AFP glycosylation heterogeneity in cancer patients with AFP-producing tumors

It has been postulated that analysis of alpha-fetoprotein (AFP) glycosylation heterogeneity in cancer patients whose AFP levels are elevated (e.g., non-seminomatous germ cell tumors, ovarian germ cell tumors and primary hepatocellular carcinoma) might provide useful clinical information. We undertook a study to determine whether scrutiny of AFP glycosylation heterogeneity in patients with non-seminomatous germ cell tumors would provide information useful in diagnosis, staging, prognosis, or monitoring for recurrence of disease following therapy. While an analysis of AFP glycosylation heterogeneity using Concanavalin A lectin chromatography did not provide useful information in regard to staging or prognosis, it does supply unique information useful in discriminating between benign liver dysfunction (e.g. alcoholic hepatitis, chemotherapy-related liver damage) and that due to nonsemininomatous germ cell tumors. It was also concluded that an analysis of Concanavalin A binding patterns is not sufficient to discriminate between recurrent non-seminomatous germ cell tumor and primary hepatocellular carcinoma in patients with elevated serum AFP.

Studies on the antigenicity and carbohydrates of human low molecular weight kininogen

Native low mol. wt (LMr) kininogen from human plasma and a kinin-free kininogen from Cohn's plasma fraction IV (HC-antigen) were isolated and studied with regard to their immunological reactivity and carbohydrate heterogeneity. Antisera were prepared against the conformational and sequence-dependent determinants of the heavy chain which is the common denominator of plasma kininogens. The molecules were characterized by single radial immunodiffusion and SDS gel electrophoresis. The effect of exoglycosidase treatment was investigated by a radioimmunoassay. It was found that the antigenic combining sites were not influenced by the partial removal of carbohydrates. These results suggest that the determinant structures of LMr kininogen reside in the peptide backbone of the protein. Carbohydrate heterogeneity was shown by different binding to concanavalin A and wheat germ lectin. With concanavalin A 52% of the immunoreactive HC-antigen was reactive compared to 76% of the native LMr kininogen. The weak reactivity (11%) of the HC-antigen towards the wheat germ lectin indicates that the N-acetylglucosamine residues are apparently blocked or missing. Immunoreactive kininogen was in all cases measured by single radial immunodiffusion or an RIA. The molecular nature of the heterogeneity is discussed in relation to the known isoelectric variations of kininogen.

Structure determination of the carbohydrate chains of rat alpha-fetoprotein

By affinity chromatography on concanavalin A (ConA) linked to Sepharose, S-carboxymethylated rat alpha-fetoprotein could be separated into two molecular variants: a ConA-reactive and a ConA-nonreactive fraction. The carbohydrate chains were quantitatively released from the protein by hydrazinolysis. Based on methylation analysis and high-resolution 1H-NMR spectroscopy of the re-N-acetylated hydrazinolysates, the carbohydrate structures of the two ConA-molecular variants of alpha-fetoprotein were established. The ConA-reactive species contains two N-glycosidic carbohydrate units per molecule, both having the following structure: (formula; see text) The ConA-nonreactive species possesses also two N-glycosidically linked oligosaccharide chains per molecule; each of these has the following structure: (formula; see text)

Characterisation of Concanavalin A-binding glycoproteins from mouse splenic leukocytes by two-dimensional electrophoresis: preferential binding of incompletely glycosylated forms of H-2 antigen to the lectin

Concanavalin A (Con A)section-binding proteins from mouse spleen leukocytes were characterised by two-dimensional electrophoresis of material precipitated, by Con A plus anti-Con A, from lysates of biosynthetically-labelled cells. Although most cell surface (iodinatable) proteins are known to bind Con A, some of the major Con A-binding proteins detected by immunoprecipitation, after a four-hour biosynthetic labelling period, are not iodinatable and are probably intracellular. Thus the major biosynthetically labelled Con A-binding species are: (i) a non-iodinatable, high molecular weight glycoprotein (C-145); (ii) intracellular precursors of secretory immunoglobulins (IgM and, probably, IgA); (iii) immature (not fully-sialylated) forms of H-2 D and K antigens; and (iv) Ia antigens. In the case of the H-2 antigens, (and possibly of other cell surface proteins) the selection of immature forms by Con A is not due to lack of biosynthetic labelling of mature products, but to preferential binding of Con A to incompletely glycosylated molecules.

Interaction of purified brush-border membrane aminopeptidase N and dipeptidyl peptidase IV with lectin-sepharose derivatives

The glycoprotein nature of two peptidases purified from the rat intestinal brush-border membrane was examined by their interaction with several lectin-Sepharose derivatives. Aminopeptidase N (EC 3.4.11.2), which contains 20% carbohydrate by weight, was bound minimally (less than 30%) by columns of Con A-, RCAI- and WGA-Sepharose. Alternatively, a greater proportion of dipeptidyl peptidase IV (EC 3.4.14.-) was bound by these immobilized lectins with 50% of the enzyme binding to Con A-Sepharose. Treatment of both enzymes with neuraminidase enhanced the binding of aminopeptidase to RCAI-Sepharose by 4-fold but did not alter the binding patterns of dipeptidyl peptidase IV. A sequential fractionation of the two peptidases with columns of Con A- and RCAI-Sepharose gave four fractions of each enzyme with differing lectin-binding specificities. Approximately 60% of the dipeptidyl peptidase IV interacted with either one or both of the lectins while only 30% of the aminopeptidase N did so. Kinetic analysis of the four isolated fractions revealed some differences, possibly related to variations in the carbohydrate moiety. The findings confirm that these two purified rat intestinal brush-border membrane peptidases are glycoproteins and, while they share a common physiologic function and source, they apparently have very different and possibly unique asparagine-linked oligosaccharide side-chains. In addition, a considerable degree of microheterogeneity exists in the carbohydrate structure of these two enzymes.

On the possible presence of a beta 2-microglobulin-like protein in extracts of livers from normal chickens and chickens with erythroblastosis--V. Studies on an immunological relationship of a small molecular weight liver protein (SMWP) to serum albumin

An extract of the livers of normal chickens (N) and chickens (Eb) infected with avian erythroblastosis virus (EbV) contained a small molecular weight protein (SMWP, mol. wt 11,000). When the extract was not dehaeminized, SMWP in agarose electrophoresis was shown to have peroxidase activity probably due to the presence of haem. When this non-dehaeminized extract was chromatographed on Con-A Sepharose neither SMWP nor an antigen (EbAg) present in Eb livers were retained. The association of EbAg with SMWP is still unexplained. Immunoelectrophoresis shows a reaction of identity between chicken SMWP and serum albumin. Chicken SMWP is thus not a beta 2-microglobulin. The finding of an immunological relationship between SMWP and albumin confirms the biochemical homology of SMWP with serum albumin in terms of amino acid residues. It has been suggested that SMWP may be a precursor or fragment of albumin but the possibility of its being a distinct entity, a microalbumin, should not be discounted.