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1.
Reactive site peptide structural similarity between heparin cofactor II and antithrombin III 总被引:6,自引:0,他引:6
Heparin cofactor II (Mr = 65,600) was purified 1800-fold from human plasma to further characterize the structural and functional properties of the protein as they compare to antithrombin III (Mr = 56,600). Heparin cofactor II and antithrombin III are functionally similar in that both proteins have been shown to inhibit thrombin at accelerated rates in the presence of heparin. There was little evidence for structural homology between heparin cofactor II and antithrombin III when high performance liquid chromatography-tryptic peptide maps and NH2-terminal sequences were compared. A partially degraded form of heparin cofactor II was also obtained in which a significant portion (Mr = 8,000) of the NH2 terminus was missing. The rates of thrombin inhibition (+/- heparin) by native and partially degraded-heparin cofactor II were not significantly different, suggesting that the NH2-terminal region of the protein is not essential either for heparin binding or for thrombin inhibition. A significant degree of similarity was found in the COOH-terminal regions of the proteins when the primary structures of the reactive site peptides, i.e. the peptides which are COOH-terminal to the reactive site peptide bonds cleaved by thrombin, were compared. Of the 36 residues identified, 19 residues in the reactive site peptide sequence of heparin cofactor II could be aligned with residues in the reactive site peptide from antithrombin III. While the similarities in primary structure suggest that heparin cofactor II may be an additional member of the superfamily of proteins consisting of antithrombin III, alpha 1-antitrypsin, alpha 1-antichymotrypsin and ovalbumin, the differences in structure could account for differences in protease specificity and reactivity toward thrombin. In particular, a disulfide bond which links the COOH-terminal (reactive site) region of antithrombin III to the remainder of the molecule and is important for the heparin-induced conformational change in the protein and high affinity binding of heparin does not appear to exist in heparin cofactor II. This observation provides an initial indication that while the reported kinetic mechanisms of action of heparin in accelerating the heparin cofactor II/thrombin and antithrombin III/thrombin reactions are similar, the mechanisms and effects of heparin binding to the two inhibitors may be different. 相似文献
2.
The location and nature of the endoproteolytic activity involved in processing of proproteins has been studied in chicken liver microsomes. A membrane-bound, calcium-dependent proteinase was found to cleave chicken proalbumin with a monobasic cleavage site approx. 10-times faster than human proalbumin, which has a dibasic cleavage site. The mutant (human) proalbumin Christchurch (Arg(-1)----Gln), with a potential monobasic site, was not processed. The enzyme, which had a pH optimum of between 5.0 and 7.0, was not inhibited by serine or aspartyl proteinase inhibitors but was affected by some inhibitors of cysteine proteinases. The convertase was specifically inhibited by the reactive centre variant alpha 1-antitrypsin Pittsburgh, but not by normal alpha 1-antitrypsin. 相似文献
3.
S D Patterson K Bell D C Shaw 《Comp. Biochem. Physiol. C, Comp. Pharmacol. Toxicol.》1991,98(2-3):359-367
1. The putative equivalent of the human major plasma serpin (alpha 1-proteinase inhibitor or alpha 1-antitrypsin) in the tammar wallaby (Macropus eugenii) has been further characterized by structural (peptide and immunopeptide mapping and sequence studies) and functional analyses revealing close homology of the wallaby proteins to human alpha 1-proteinase inhibitor. 2. A sixth allele, Pi J, was detected and its products characterized in terms of pI, Mr, inhibitory spectra and terminal sialic acid content. 3. A recently-developed electrophoretic in situ oxidation/binding method was adapted to provide protein suitable for sequence analysis of the N-terminus and reactive site region including assignment of the P1 and P'1 residues. 4. All sequence analyses were performed on proteins or peptides (approximately Mr 3500) blotted onto polybrene treated GF/C or polyvinylidene difluoride membrane respectively. 5. The P5 to P'4 residues of the reactive centre are identical with those of the human inhibitor thereby allowing the wallaby inhibitor also to be classified as a METserpin. 6. The P1 methionine is presumably responsible for the oxidation sensitivity observed in the electrophoretic in situ functional assay for the wallaby inhibitor. 7. The plasma concentration of the wallaby inhibitor is similar to that reported for human alpha 1-proteinase inhibitor. 相似文献
4.
L F Kress 《Journal of cellular biochemistry》1986,32(1):51-58
Human plasma serine proteinase inhibitors (serpins) gradually lost activity when incubated with catalytic amounts of snake venom or bacterial metalloproteinases. Electrophoretic analyses indicated that antithrombin III, C1-inhibitor, and alpha 2-antiplasmin had been converted by limited proteolysis into modified species which retained inhibitory activity. Further proteolytic attack resulted in the formation of inactivated inhibitors; alpha 1-proteinase inhibitor (alpha 1-antitrypsin) and alpha 1-antichymotrypsin were also enzymatically inactivated, but active intermediates were not detected. Sequence analyses indicated that the initial, noninactivating cleavage occurred in the amino-terminal region of the inhibitors. Inactivation resulted in all cases from the limited proteolysis of a single bond near, but not at, the reactive site bond in the carboxy-terminal region of the inhibitors. The results indicate that the serpins have two regions which are susceptible to limited proteolysis--one near the amino-terminal end and another in the exposed reactive site loop of the inhibitor. 相似文献
5.
Chemical modifications of human plasma alpha1-antitrypsin with reagents which modify lysyl residues (citraconic anhydride, acetic anhydride, formaldehyde and 2,4,6-trinitrobenzenesulfonic acid) and arginyl residued (1,2-cyclohexanedione) were examined with regard to their effect upon the elastase inhibitory capacity of the glycoprotein. 2,4,6-Trinitrobenzenesulfonic acid was employed to quantitate the remaining free amino groups (epsilon-NH2 groups of lysine) and the extent of modifications. Amino acid analysis was utilized in the same capacity for the guanidino groups of arginyl residues. The elastase inhibitory capacity of alpha1-antitrypsin was destroyed following trinitrophenylation, citraconylation and acetylation. Circular dichroism of the native and modified derivatives revealed major changes in conformation following trinitrophenylation and citraconylation while CD profiles of acetylated and reductively methylated derivatives differed from that of the native profile considerably less. Reductively methylated alpha1-antitrypsin retained its elastatse inhibitory capacity. The reaction of 1,2-cyclohexanedione with alpha1-antitrypsin did not effect in a loss in inhibitory capacity. Gel filtration studies of native and modified alpha1-antitrypsin on Sephadex G-100 demonstrated an increased molecular weight presumably through molecular aggregation, in the citraconylated and trinitrophenylated derivatives, but not in the cases of the other derivatives. Based upon these studies and previous investigations of our laboratory, it was concluded that (1) alpha1-antitrypsin is a lysyl inhibitor type (i.e., the reactive site is a Lys-X bond), (2) its interaction with elastase follows a pattern similar to trypsin and chymotrypsin, and (3) the positively charged epsilon-NH2 group of lysine is essential for the maintenance of elastase inhibitory capacity. 相似文献
6.
Sivasothy P Dafforn TR Gettins PG Lomas DA 《The Journal of biological chemistry》2000,275(43):33663-33668
alpha(1)-Antitrypsin is the most abundant circulating protease inhibitor and the archetype of the serine protease inhibitor or serpin superfamily. Members of this family may be inactivated by point mutations that favor transition to a polymeric conformation. This polymeric conformation underlies diseases as diverse as alpha(1)-antitrypsin deficiency-related cirrhosis, thrombosis, angio-edema, and dementia. The precise structural linkage within a polymer has been the subject of much debate with evidence for reactive loop insertion into beta-sheet A or C or as strand 7A. We have used site directed cysteine mutants and fluorescence resonance energy transfer (FRET) to measure a number of distances between monomeric units in polymeric alpha(1)-antitrypsin. We have then used a combinatorial approach to compare distances determined from FRET with distances obtained from 2.9 x 10(6) different possible orientations of the alpha(1)-antitrypsin polymer. The closest matches between experimental FRET measurements and theoretical structures show conclusively that polymers of alpha(1)-antitrypsin form by insertion of the reactive loop into beta-sheet A. 相似文献
7.
Ravi Mahadeva Timothy R Dafforn Robin W Carrell David A Lomas 《The Journal of biological chemistry》2002,277(9):6771-6774
Conformational diseases such as amyloidosis, Alzheimer's disease, prion diseases, and the serpinopathies are all caused by structural rearrangements within a protein that transform it into a pathological species. These diseases are typified by the Z variant of alpha(1)-antitrypsin (E342K), which causes the retention of protein within hepatocytes as inclusion bodies that are associated with neonatal hepatitis and cirrhosis. The inclusion bodies result from the Z mutation perturbing the conformation of the protein, which facilitates a sequential interaction between the reactive center loop of one molecule and beta-sheet A of a second. Therapies to prevent liver disease must block this reactive loop-beta-sheet polymerization without interfering with other proteins of similar tertiary structure. We have used reactive loop peptides to explore the differences between the pathogenic Z and normal M alpha(1)-antitrypsin. The results show that the reactive loop is likely to be partially inserted into beta-sheet A in Z alpha(1)-antitrypsin. This conformational difference from M alpha(1)-antitrypsin was exploited with a 6-mer reactive loop peptide (FLEAIG) that selectively and stably bound Z alpha(1)-antitrypsin. The importance of this finding is that the peptide prevented the polymerization of Z alpha(1)-antitrypsin and did not significantly anneal to other proteins (such as antithrombin, alpha(1)-antichymotrypsin, and plasminogen activator inhibitor-1) with a similar tertiary structure. These findings provide a lead compound for the development of small molecule inhibitors that can be used to treat patients with Z alpha(1)-antitrypsin deficiency. Furthermore they demonstrate how a conformational disease process can be selectively inhibited with a small peptide. 相似文献
8.
N-terminal amino acid sequences of precursor and mature forms of alpha-1-antitrypsin 总被引:1,自引:0,他引:1
V Gross C Kaiser T A Tran-Thi E Schmelzer I Witt T H Plummer P C Heinrich 《FEBS letters》1983,151(2):201-205
alpha-1-Antitrypsin is found in hepatocytes as a high-mannose glycoprotein (Mr 49 000), extracellularly as a complex-type glycoprotein (Mr 54 000). Deglycosylation of both forms with peptide: N-glycosidase led to proteins of identical app. Mr (41 000). The sequence of 26 N-terminal amino acids of rat alpha 1-antitrypsin was determined. A high content of polar amino acids was found. The partially characterized presequence of in vitro synthesized alpha 1-antitrypsin showed a cluster of hydrophobic amino acids. A pre-peptide of 24 amino acids is proposed. There is no evidence for the existence of a propeptide. 相似文献
9.
Expression of human alpha 1-antitrypsin in Escherichia coli 总被引:2,自引:0,他引:2
10.
The native forms of common globular proteins are in their most stable state but the native forms of plasma serpins (serine protease inhibitors) show high energy state interactions. The high energy state strain of alpha(1)-antitrypsin, a prototype serpin, is distributed throughout the whole molecule, but the strain that regulates the function directly appears to be localized in the region where the reactive site loop is inserted during complex formation with a target protease. To examine the functional role of the strain at other regions of alpha(1)-antitrypsin, we increased the stability of the molecule greatly via combining various stabilizing single amino acid substitutions that did not affect the activity individually. The results showed that a substantial increase of stability, over 13 kcal mol(-1), affected the inhibitory activity with a correlation of 11% activity loss per kcal mol(-1). Addition of an activity affecting single residue substitution in the loop insertion region to these very stable substitutions caused a further activity decrease. The results suggest that the native strain of alpha(1)-antitrypsin distributed throughout the molecule regulates the inhibitory function in a concerted manner. 相似文献
11.
A cell-specific enhancer of the mouse alpha 1-antitrypsin gene has multiple functional regions and corresponding protein-binding sites. 总被引:13,自引:10,他引:13
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D R Grayson R H Costa K G Xanthopoulos J E Darnell Jr 《Molecular and cellular biology》1988,8(3):1055-1066
We have previously described the isolation and characterization of genomic clones corresponding to the mouse alpha 1-antitrypsin gene (Krauter et al., DNA 5:29-36, 1986). In this report, we have analyzed the DNA sequences upstream of the RNA start site that direct hepatoma cell-specific expression of this gene when incorporated into recombinant plasmids. The 160 nucleotides 5' to the cap site direct low-level expression in hepatoma cells, and sequences between -520 and -160 bp upstream of the RNA start site functioned as a cell-specific enhancer of expression both with the alpha 1-antitrypsin promoter and when combined with a functional beta-globin promoter. Within the enhancer region, three binding sites for proteins present in hepatoma nuclear extracts were identified. The location of each site was positioned, using both methylation protection and methylation interference experiments. Each protein-binding site correlated with a functionally important region necessary for full enhancer activity. These experiments demonstrated a complex arrangement of regulatory elements comprising the alpha 1-antitrypsin enhancer. Significant qualitative differences exist between the findings presented here and the cis-acting elements operative in regulating expression of the human alpha 1-antitrypsin gene (Ciliberto et al., Cell 41:531-540, 1985; De Simone et al., EMBO J. 6:2759-2766, 1987). 相似文献
12.
Reactivity of alpha 1-antitrypsin mutants against proteolytic enzymes of the kallikrein-kinin, complement, and fibrinolytic systems 总被引:2,自引:0,他引:2
P A Patston N Roodi J A Schifferli R Bischoff M Courtney M Schapira 《The Journal of biological chemistry》1990,265(18):10786-10791
Increased extracellular proteolysis because of unregulated activation of blood coagulation, complement, and fibrinolysis is observed in thrombosis, shock, and inflammation. In the present study, we have examined whether the plasma kallikrein-kinin system, the classical pathway of complement, and the fibrinolytic system could be inhibited by alpha 1-antitrypsin reactive site mutants. Wild-type alpha 1-antitrypsin contains a Met residue at P1 (position 358), the central position of the reactive center. It did not inhibit plasma kallikrein, beta-factor XIIa, plasmin, tissue-type plasminogen activator (t-PA), or urokinase. In contrast, these serine proteases were inhibited by alpha 1-antitrypsin Arg358. For the inhibition of C1s, a double mutant having Arg358 and a Pro----Ala mutation at P2 (position 357) was required. This double modification was made because C1-inhibitor, the natural inhibitor of C1s, has Arg and Ala residues at positions P1 and P2. Plasminogen activator inhibitor 1, the natural inhibitor of t-PA, also has Arg and Ala residues at positions P1 and P2. In a purified system, alpha 1-antitrypsin Ala357-Arg358 was 150-fold less efficient against C1s than C1-inhibitor and 27,000-fold less efficient against t-PA than plasminogen activator inhibitor-1. In plasma, 2.3 microM alpha 1-antitrypsin Ala357-Arg358 reduced by 65% the formation of a complex between kallikrein and C1-inhibitor following activation of the intrinsic pathway of blood coagulation by kaolin. Furthermore, after supplementation by 2.0 microM alpha 1-antitrypsin Ala357-Arg358, zymographic analysis showed that the majority of the free t-PA of normal plasma formed a bimolecular complex with the double mutant. In contrast, 3.4 microM alpha 1-antitrypsin Ala357-Arg358 did not prevent the activation of the classical pathway of complement observed when normal serum is supplemented with anti-C1-inhibitor F(ab')2 fragment. These results demonstrate that alpha 1-antitrypsin Ala357-Arg358 has therapeutic potential for disorders with unregulated activation of the intrinsic pathway of blood coagulation and the fibrinolytic system; however, the double mutant is not an efficient inhibitor for the classical pathway of complement. 相似文献
13.
R W Berninger M F Teixeira 《Comparative biochemistry and physiology. B, Comparative biochemistry》1986,85(2):325-332
Rhesus monkey alpha 1-antitrypsin (n = 144) was examined for heterogeneity by acid starch gel electrophoresis, isoelectric focusing in agarose and agarose gel electrophoresis. In contrast to other studies, no heterogeneity of Rhesus monkey alpha 1-antitrypsin could be documented using specific antisera. Rhesus monkey alpha 1-antitrypsin contained a reactive thiol. The pIs of the major isoforms of Rhesus monkey alpha 1-antitrypsin were 4.63, 4.69, 4.84 and 4.86 at 4 degrees C. No deficiency state of Rhesus monkey alpha 1-antitrypsin was detected. The six protease inhibitors in Rhesus monkey sera cross-reacted with antisera to the six human protease inhibitors. 相似文献
14.
Conditions under which the glycosylation capacity of cells is limited provide an opportunity for studying the efficiency of site-specific glycosylation and the role of glycosylation in the maturation of glycoproteins. Congenital disorders of glycosylation type 1 (CDG-I) provide such a system. CDG-I is characterized by underglycosylation of glycoproteins due to defects in the assembly or transfer of the common dolichol-pyrophosphate-linked oligosaccharide precursor of asparagine-linked glycans. Human plasma alpha1-antitrypsin is normally fully glycosylated at three asparagine residues (46, 83, and 247), but un-, mono-, di-, and fully glycosylated forms of alpha1-antitrypsin were detected by 2D PAGE in the plasma from patients with CDG-I. The state of glycosylation of the three asparagine residues was analyzed in all the underglycosylated forms of alpha1-antitrypsin by peptide mass fingerprinting using matrix-assisted laser desorption ionization time-of-flight mass spectrometry. It was found that asparagine 46 was always glycosylated and that asparagine 83 was never glycosylated in the underglycosylated glycoforms of alpha1-antitrypsin. This showed that the asparagine residues are preferentially glycosylated in the order 46>247>83 in the mature underglycosylated forms of alpha1-antitrypsin found in plasma. It is concluded that the nonoccupancy of glycosylation sites is not random under conditions of decreased glycosylation capacity and that the efficiency of glycosylation site occupancy depends on structural features at each site. The implications of this observation for the intracellular transport and sorting of glycoproteins are discussed. 相似文献
15.
Dunstone MA Dai W Whisstock JC Rossjohn J Pike RN Feil SC Le Bonniec BF Parker MW Bottomley SP 《Protein science : a publication of the Protein Society》2000,9(2):417-420
Alpha1-antitrypsin deficiency, which can lead to both emphysema and liver disease, is a result of the accumulation of alpha1-antitrypsin polymers within the hepatocyte. A wealth of biochemical and biophysical data suggests that alpha1-antitrypsin polymers form via insertion of residues from the reactive center loop of one molecule into the beta-sheet of another. However, this long-standing hypothesis has not been confirmed by direct structural evidence. Here, we describe the first crystallographic evidence of a beta-strand linked polymer form of alpha1-antitrypsin: the crystal structure of a cleaved alpha1-antitrypsin polymer. 相似文献
16.
N A Kalsheker I J Hodgson G L Watkins J P White H M Morrison R A Stockley 《BMJ (Clinical research ed.)》1987,294(6586):1511-1514
Specific gene probes were used to study restriction fragment length polymorphisms of the human alpha 1-antitrypsin gene. A polymorphism due to loss of a recognition site for the restriction enzyme Taq I was identified in eight of 42 patients with bronchiectasis and nine of 49 patients with pulmonary emphysema, none of whom had alpha 1-antitrypsin deficiency. Among a control group without lung disease the polymorphism was significantly less frequent, being found in only five of 101 apparently healthy blood donors. The deoxyribonucleic acid (DNA) polymorphism was also present in two of 14 unrelated patients with alpha 1-antitrypsin deficiency, indicating a lack of association with any specific alpha 1-antitrypsin protein phenotype. The polymorphism identified in this study may be a new marker for genetic predisposition to chronic lung disease. 相似文献
17.
A cDNA clone encoding rat alpha 1-antitrypsin has been isolated from a lambda gt-11 rat liver cDNA library using an antigen-overlay immunoscreening method. The nucleotide sequence of this cDNA clone is 1306 base pairs in length and has a coding region of 1224 base pairs which can be translated into an alpha 1-antitrypsin precursor protein consisting of 408 amino acid residues. The cDNA sequence contains a termination codon, TAA, at position 1162 and a polyadenylation signal sequence, AATAAT, at position 1212. The calculated molecular weight of the translated mature protein is 43,700 with 387 amino acid residues; this differs from purified rat alpha 1-antitrypsin's apparent molecular weight of 54,000 because of glycosylation. Five potential glycosylation sites were identified on the basis of the cDNA sequence. The translated mature protein sequence from the cDNA clone matches completely with the N-terminal 33 amino acids of purified rat alpha 1-antitrypsin, which has an N-terminal Glu. The cDNA encoding rat alpha 1-antitrypsin shares 70% and 80% sequence identity with its human and mouse counterparts, respectively. The reactive center sequence of rat alpha 1-antitrypsin is highly conserved with respect to human alpha 1-antitrypsin, both having Met-Ser at the P1 and P1' residues. Genomic Southern blot analysis yielded a simple banding pattern, suggesting that the rat alpha 1-antitrypsin gene is single-copy. Northern blot analysis using the cDNA probe showed that rat alpha 1-antitrypsin is expressed at high levels in the liver and at low levels in the submandibular gland and the lung.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
18.
Identification and some properties of a new fast-reacting plasmin inhibitor in human plasma. 总被引:11,自引:0,他引:11
D Collen 《European journal of biochemistry》1976,69(1):209-216
Fresh plasma was seeded with trace amounts of highly purified biologically intact iodine-labelled plasminogen and the plasmin-inhibitor complexes formed after activation with streptokinase or urokinase separated by gel filtration. Two radioactive peaks were observed, the first one eluted in the void volume and the second one just before the 7-S globulin peak. In incompletely activated samples, the second peak was always predominant over the first one. Both components were purified with high yield by a combination of affinity chromatography on lysine-agarose and gel filtration, and investigated by dodecylsulphate-polyacrylamide gel electrophoresis and immunoelectrophoresis. Neither component reacted with antisera against alpha1-antitrypsin, antithrombin III, C1-esterase inhibitor, inter-alpha-trypsin inhibitor or alpha1-antichymotrypsin. The component of the first peak appeared to be a complex between plasmin and alpha2-macroglobulin which reacted with antisera against human plasminogen and against alpha2-macroglobulin. The component of the second peak had a molecular weight (Mr) of 120000-140000 by dodecyl-sulphate-polyacrylamide gel electrophoresis and lpon reduction displayed a doublet band with an Mr of 65000-70000 and a band with Mr 11000. It reacted with antisera against plasminogen and with antisera raised against this complex and absorbed with purified plasminogen. The latter antisera reacted with a single component in plasma which is different from the above-mentioned plasma protease inhibitors. Specific removal of this component from plasma by immuno-absorption resulted in disappearance of the fast-reacting antiplasmin activity whereas alpha2-macroglobulin was found to represent the slower-reacting plasmin-neutralizing activity. In the presence of normal plasma levels of these proteins, the specific removal or absence of alpha1-antitrypsin, antithrombin III or C1-esterase inhibitor did not alter the inactivation rate of plasmin when added to plasma in quimolar amounts to that of plasminogen. It is concluded that only two plasma proteins are important in the binding of plasmin generated by activation of the plasma plasminogen, namely a fast-reacting inhibitor which is different from the known plasma protease inhibitors and which we have provisionally named antiplasmin, and alpha2-macroglobulin, which reacts more slowly. 相似文献
19.
The rate of synthesis of alpha 1-antitrypsin has been studied in organ cultures of fetal human liver. By de novo synthesis, alpha 1-antitrypsin of the same electrophoretic mobility and molecular size as plasma alpha 1-antitrypsin was produced. Synthetic rate was comparable to in vivo conditions and was suppressed by cycloheximide, colchicine and neuraminidase. By increasing alpha 1-antitrypsin levels in cultre medium, suppression of alpha 1-antitrypsin release from the intra-to the extracellular site was achieved, i.e., synthesis does not proceed autonomously. This suppression was preceded by a temporary enhancement of synthesis. Both effects were found to be independent of degree of sialylation of add-d alpha 1-antitrypsin. In contrast to alpha 1-antitrypsin released in tissue culture, the intracellular protein, as analyzed by crossed immunoelectrophoresis of Triton X-100 extracts from fetal liver, was found to occur partly as slowly moving peaks. Whether these peaks represent proforms or incompletely glycosylated precursors of export alpha 1-antitrypsin or complexes with proteases remains unsettled. A variety of other plasma proteins are released in organ cultures making the system suitable for study of factors regulating plasma protein synthesis. 相似文献
20.
Xenopus oocytes can synthesise but do not secrete the Z variant of human alpha 1-antitrypsin 总被引:7,自引:0,他引:7
Human liver mRNA was prepared from a patient homozygous for alpha 1-antitrypsin deficiency (PiZZ) and from a normal subject (PiMM). Both liver RNAs were microinjected into Xenopus oocytes and alpha 1-antitrypsin identified by immunoprecipitation. The normal M variant of alpha 1-antitrypsin is synthesised and secreted by Xenopus oocytes, the abnormal Z protein is not secreted and an intracellular form accumulates in the oocytes. In the presence of tunicamycin an unglycosylated form of M alpha 1-antitrypsin appears in the incubation medium but no corresponding unglycosylated version of the Z protein is secreted. 相似文献