Search PubMed⌕ Search

Biomedical subjects

L Wu

Publications and source records attributed to L Wu.

At least 19 recordsLinked to original sources
PubMed1997

Chemokine receptor usage by human eosinophils. The importance of CCR3 demonstrated using an antagonistic monoclonal antibody.

Chemokines bind and signal through G-protein coupled seven transmembrane receptors. Various chemokine receptors are expressed on leukocytes, and these may impart selective homing of leukocyte subsets to sites of inflammation. Human eosinophils express the eotaxin receptor, CCR3, but respond to a variety of CC chemokines apart from eotaxin, including RANTES, monocyte chemotactic protein (MCP)-2, MCP-3, and MCP-4. Here we describe a mAb, 7B11, that is selective for CCR3 and has the properties of a true receptor antagonist. 7B11 blocked binding of various radiolabeled chemokines to either CCR3 transfectants, or eosinophils. Pretreatment of eosinophils with this mAb blocked chemotaxis and calcium flux induced by all CCR3 ligands. In all individuals examined, including allergic and eosinophilic donors, > 95% of the response of eosinophils to eotaxin, RANTES, MCP-2, MCP-3, and MCP-4 was shown to be mediated through CCR3. The IL-8 receptors, particularly CXCR2, were induced on IL-5 primed eosinophils, however these eosinophils responded to CC chemokines in the same manner as unprimed eosinophils. These results demonstrate the importance of CCR3 for eosinophil responses, and the feasibility of completely antagonizing this receptor.

Antibodies, Monoclonal↗
PubMed1997

Gene-based neurotransmitter modulation in cerebellar granule neurons.

The human glutamic acid decarboxylase (GAD) gene was transferred into rat cerebellar granule neurons. Following adenoviral-mediated gene transfer, nearly 100% of the neurons had transgene expression that persisted for the duration of their survival in culture. GABA levels were elevated both in the growth media and in lysates of GAD-modified granule neurons. In GAD-modified neurons, extracellular GABA levels steadily increased with time, whereas intracellular GABA levels peaked 10 days after gene transfer. GAD-modified neurons released both glutamate and GABA into the surrounding media before and after potassium-induced stimulation, but only the release of glutamate was sensitive to potassium stimulation. These data suggest that glutamatergic neurons, which initially contained no detectable GABA, can be genetically modified to release GABA constitutively.

Adenoviridae↗
PubMed1997

Roles of Wee1 and Nim1 protein kinases in regulating the switch from mitotic division to sexual development in Schizosaccharomyces pombe.

In self-fertile strains of the fission yeast Schizosaccharomyces pombe, nitrogen starvation initiates a program of sexual development in which cells express mating pheromones and receptors, arrest cell cycle progression in G1, and conjugate. This process is dependent on Rum1, an inhibitor of the Cdc2-Cdc13 and Cdc2-Cig2 cyclin B kinases. The M-phase induction activity of Cdc2-Cdc13 is inhibited by Wee1 tyrosine kinase, which phosphorylates Cdc2 on tyrosine-15. We report here that Wee1 activity is also important for mating. This discovery arose from studies of Nim1, a kinase which promotes mitosis by inhibiting Wee1. Nim1 was previously thought to have an important role in promoting mitosis during nitrogen starvation, but our studies revealed that Nim1 protein drops to an undetectable level within 15 min of nitrogen depletion. In contrast, Wee1 remains abundant, and tyrosine-phosphorylated Cdc2 is detected for at least 4 h after resuspension of cells in nitrogen-free medium. This suggested that maintenance of Wee1 activity may be important during the early stages of nitrogen starvation, a proposal confirmed by the observation that mating efficiency is reduced ca. fivefold in wee1- cells. Transcriptional induction of genes encoding mating factors and receptors is also delayed in wee1- cells. The wee1- mating defect is suppressed by deletion of cig2+, which encodes a B-type cyclin that promotes the onset of S and inhibits conjugation. These findings indicate that Wee1 and Rum1 act jointly to inhibit Cdc2 and promote sexual development in nitrogen-starved cells.

Ammonium Chloride↗
PubMed1996

Discrete steps in binding and signaling of interleukin-8 with its receptor.

The mechanisms by which chemokines bind and signal through their receptors are complex and poorly understood. In the present study, we sought to dissect these processes and to map important functional domains of the two CXC chemokine (interleukin-8) receptors, CXCR1 (formally IL-8RA) and CXCR2 (formally IL-8RB), using blocking monoclonal antibodies (mAbs) to the receptors and a series of chimeras between CXCR1 and CXCR2. A panel of specific mAbs against CXCR1 or CXCR2, generated by immunizing mice with transfectants expressing either receptor, were shown to effectively block IL-8- and/or growth-related oncogene alpha (GROalpha) -mediated ligand binding, chemotaxis, elastase release, and VCAM-1 binding in CXCR1 and CXCR2 transfectants and/or human neutrophils. Of particular interest was an anti-CXCR1 mAb, 7D9, that inhibited chemotaxis, elastase release, and VCAM-1 binding but had no detectable effects on ligand binding. The epitopes of these blocking mAbs were mapped by using a series of CXCR1/2 chimera transfectants and synthetic peptides. Most of the anti-CXCR1 antibodies, except 7D9, mapped to the amino acid sequence WDFDDL (CXCR1 residues 10-15), and all the anti-CXCR2 antibodies mapped to the amino acid sequence FEDFW (CXCR2 residues 6-10). The epitope of mAb 7D9 mainly involved a region within the first 45 residues of CXCR1, and it appeared to be conformation-sensitive. These results support a model in which the binding and signaling of IL-8 with its receptor occur in at least two discrete steps involving distinct domains of the receptor. This model is consistent with the notion that discrete conformational changes of the receptor secondary to ligand binding are required to trigger various biological responses. Moreover, the ligand binding and chemotaxis properties of each CXCR1/2 chimeric receptor to IL-8 and GROalpha were determined. It was found that each is distinct in its ability to confer ligand binding and chemotactic response to IL-8 and GROalpha, and two conclusions could be made. 1) The N-terminal segment of CXCR1 is a dominant determinant of receptor subtype selectivity, consistent with previous studies using rabbit/human CXCR1/2 chimeras; and 2) the specificity determinant for GROalpha binding in CXCR2 involves sequences in the N terminus, distal to the first 15 residues, as well as other parts of the receptor.

Amino Acid Sequence↗
PubMed1996

Dendritic cell development in culture from thymic precursor cells in the absence of granulocyte/macrophage colony-stimulating factor.

The earliest lymphoid precursor population in the adult mouse thymus had previously been shown to produce not only T cells, but also dendritic cell (DC) progeny on transfer to irradiated recipients. In this study, culture of these isolated thymic precursors with a mixture of cytokines induced them to proliferate and to differentiate to DC, but not to T lineage cells. At least 70% of the individual precursors had the capacity to form DC. The resultant DC were as effective as normal thymic DC in the functional test of T cell stimulation in mixed leukocyte cultures. The cultured DC also expressed high levels of class I and class II major histocompatibility complex, together with CD11c, DEC-205, CD80, and CD86, markers characteristic of mature DC in general. However, they did not express CD8 alpha or BP-1, markers characteristic of normal thymic DC. The optimized mixture of five to seven cytokines required for DC development from these thymic precursors did not include granulocyte/macrophage colony stimulating factor (GM-CSF), usually required for DC development in culture. The addition of anti-GM-CSF antibody or the use of precursors from GM-CSF-deficient mice did not prevent DC development. Addition of GM-CSF was without effect on DC yield when interleukin (IL) 3 and IL-7 were present, although some stimulation by GM-CSF was noted in their absence. In contrast, DC development was enhanced by addition of the Flt3/Flk2 ligand, in line with the effects of the administration of this cytokine in vivo. The results indicate that the development of a particular lineage of DC, probably those of lymphoid precursor origin, may be independent of the myeloid hormone GM-CSF.

Animals↗
PubMed1996

CD4-induced interaction of primary HIV-1 gp120 glycoproteins with the chemokine receptor CCR-5.

For efficient entry into target cells, primary macrophage-tropic and laboratory-adapted human immunodeficiency viruses type 1 (HIV-1) require particular chemokine receptors, CCR-5 and CXCR-4, respectively, as well as the primary receptor CD4 (refs 1-6). Here we show that a complex of gp120, the exterior envelope glycoprotein, of macrophage-tropic primary HIV-1 and soluble CD4 interacts specifically with CCR-5 and inhibits the binding of the natural CCR-5 ligands, macrophage inflammatory protein (MIP)-1alpha and MIP-1beta (refs 7, 8). The apparent affinity of the interaction between gp120 and CCR-5 was dramatically lower in the absence of soluble CD4. Additionally, in the absence of gp120, an interaction between a two-domain CD4 fragment and CCR-5 was observed. A gp120 fragment retaining the CD4-binding site and overlapping epitopes was able to interact with CCR-5 only if the V3 loop, which can specify HIV-1 tropism and chemokine receptor choice, was also present on the molecule. Neutralizing antibodies directed against either CD4-induced or V3 epitopes on gp120 blocked the interaction of gp12O-CD4 complexes with CCR-5. These results suggest that HIV-1 attachment to CD4 creates a high-affinity binding site for CCR-5, leading to membrane fusion and virus entry.

Animals↗
PubMed1996

Adenovirus-mediated gene transfer in the transplant setting: early events after orthotopic transplantation of liver allografts expressing TGF-beta1.

We hypothesized that adenovirus mediated gene transfer of TGF-beta1 into liver grafts would enhanced local expression of this recombinant protein and down-regulate inflammatory and alloreactive immune response. A full length DNA encoding the murine TGF-beta1 was used to replaced the E1 region of adenovirus type 5 (AdmTGF-beta1). Expression and protein production of biologically active murine TGF-beta1 was tested in AdmTGF-beta1-transduced Hep G2 cells and TGF-beta-sensitive MV1 cells. In the transplant setting, the replication-defective vector was used to perfused cold preserved ACI liver allograft prior to transplantation into Lewis recipients. Control livers were similarly perfused with cold lactated Ringer's solution and were followed without immunosuppression. Animals were sacrificed at 1, 3, and 5 days after transplantation. Intragraft cytokine levels of TNFalpha, and IFNgamma were determined using ELISA and quantitative PCR. TGF-beta1 ELISA of culture supernatants from AdmTGF-beta1 transduced hepatocyte cell line Hep G2 excreted TGF-beta1 in quantities directly correlated with multiplicity of infection (MOI, vector:hepatic cell ratio). The biological activity of the excreted recombinant protein was confirmed by growth inhibition of MV1 TGF-beta-sensitive cells. Enhanced production of TGF-beta1 in transduced allografts was associated with decreased levels of TNFalpha and IFNgamma when compared with nonimmunosuppressed controls. Adenovirus-mediated gene transfer of murine TGF-beta1 into hepatic cells results in the expression of biologically active protein. Transduction of allografts with TGF-beta1 down-regulates TNFalpha and IFNgamma production early after orthotopic transplantation. Graft transduction with TGF-beta1 offers a novel approach to study the effects of single immune modulator on alloreactive immune response, T cell function, and cytokine cascade.

Adenoviridae↗
PubMed1996

Cytoplasmic polyadenylation of activin receptor mRNA and the control of pattern formation in Xenopus development.

The activin receptor, a transmembrane serine-threonine kinase, is a key component necessary for pattern formation in early Xenopus development. This protein interacts with members of the transforming growth factor beta family and stimulates cells of the marginal zone to differentiate along the mesodermal pathway. In large part, this function of the activin receptor has been inferred from observations of phenotypes induced by injected mRNA encoding wild-type or mutant forms of the protein. Naturally occurring activin receptor mRNA is maternally inherited and contains within its 3' untranslated region an embryonic-type cytoplasmic polyadenylation element (CPE), an oligouridylic acid sequence that promotes cytoplasmic polyadenylation and resultant translational activation. Based on the presence of this element, we predicted in a previous report that activin receptor mRNA expression in embryos might be regulated by cytoplasmic polyadenylation (Simon and Richter, Mol. Cell. Biol. 14, 7867-7875, 1994). In this study, we have tested this hypothesis and show that not only do endogenous and injected activin receptor mRNAs undergo cytoplasmic polyadenylation during embryogenesis, but also that this process is necessary for stimulating translation and inducing the morphological defects observed by mRNA overexpression. The activin receptor CPE is bound by a Mr 36 x 10(3) protein in vitro, and competition for this factor between mRNAs in vivo inhibits activin receptor mRNA polyadenylation. This competition may be responsible for the lack of mesoderm formation observed in such injected embryos. These data suggest that cytoplasmic polyadenylation controls differentiation and pattern formation in early Xenopus development.

Activin Receptors↗
PubMed1996

The beta-chemokine receptors CCR3 and CCR5 facilitate infection by primary HIV-1 isolates.

We examined the ability of chemokine receptors and related G protein-coupled receptors to facilitate infection by primary, clinical HIV-1 isolates. CCR5, when expressed along with CD4, the HIV-1 receptor, allowed cell lines resistant to most primary HIV-1 isolates to be infected. CCR3 facilitated infection by a more restricted subset of primary viruses, and binding of the CCR3 ligand, eotaxin, inhibited infection by these isolates. Utilization of CCR3 and CCR5 on the target cell depended upon the sequence of the third variable (V3) region of the HIV-1 gp120 exterior envelope glycoprotein. The ability of various members of the chemokine receptor family to support the early stages of HIV-1 infection helps to explain viral tropism and beta-chemokine inhibition of primary HIV-1 isolates.

Acquired Immunodeficiency Syndrome↗
PubMed1996

Molecular cloning and characterization of a human eotaxin receptor expressed selectively on eosinophils.

The chemokine eotaxin is unusual in that it appears to be a highly specific chemoattractant for eosinophils. Ligand-binding studies with radiolabeled eotaxin demonstrated a receptor on eosinophils distinct from the known chemokine receptors CKR-1 and -2. The distinct eotaxin binding site on human eosinophils also bound RANTES (regulated on activation T expressed and secreted) and monocyte chemotactic protein (MCP)3. We have now isolated a cDNA from eosinophils, termed CKR-3, with significant sequence similarity to other well characterized chemokine receptors. Cells transfected with CKR-3 cDNA bound radiolabeled eotaxin specifically and with high affinity, comparable to the binding affinity observed with eosinophils. This receptor also bound RANTES and MCP-3 with high affinity, but not other CC or CXC chemokines. Furthermore, receptor transfectants generated in a murine B cell lymphoma cell line migrated in transwell chemotaxis assays to eotaxin, RANTES, and MCP-3, but not to any other chemokines. A monoclonal antibody recognizing CKR-3 was used to show that eosinophils, but not other leukocyte types, expressed this receptor. This pattern of expression was confirmed by Northern blot with RNA from highly purified leukocyte subsets. The restricted expression of CKR-3 on eosinophils and the fidelity of eotaxin binding to CKR-3, provides a potential mechanism for the selective recruitment and migration of eosinophils within tissues.

Amino Acid Sequence↗
PubMed1996

Probing the function of Asp128 in the lower molecular weight protein-tyrosine phosphatase-catalyzed reaction. A pre-steady-state and steady-state kinetic investigation.

The role of Asp128 in the catalytic mechanism of the low Mr protein-tyrosine phosphatase (PTPase) from the fission yeast Schizosaccharomyces pombe has been investigated by a combination of site-directed mutagenesis and pre-steady-state and steady-state kinetic analysis. The corresponding aspartic acid in the bovine enzyme is located on a loop adjacent to the phosphate-binding loop and forms a hydrogen bond with the oxygen atom of the bound sulfate or phosphate that is structurally homologous to the ester oxygen in substrates [Su et al. (1994) Nature 370, 575-578; Zhang, M., et al. (1994) Biochemistry 33, 11097-11105]. Asp128 has been replaced by a Glu, an Asn, and an Ala. The kcat for the hydrolysis of p-nitrophenyl phosphate (pNPP) decreases by factors of 6.7, 400, and 650 for the mutants D128E, D128N, and D128A, respectively. Compared to the wild type, the binding affinity for phosphate is decreased 2 and 4.3-fold, respectively, for the D128A and D128N mutants, whereas no change in affinity is observed for the D128E mutant. An evaluation of the burst kinetics demonstrates that Asp128 plays a role in both the phosphoenzyme intermediate formation (k2) and breakdown (k3). Thus, substitution at Asp128 by a Glu, an Asn, or an Ala reduces k2 by 17, 7480, and 11900 and reduces k3 by 6.2, 380, and 40. The greater effect on k2 and k3 is consistent with a dissociative transition-state for the low M(r)PTPase-catalyzed reaction. Results from the rapid kinetics, partition experiments, and leaving group dependence experiments suggest that for the wild type and D128E mutant, the rate-limiting step is k3, whereas k2 has become rate-limiting for the D128N mutant. With the exception of pNPP, k2 may also be rate-limiting for D128A. Taken together, these results are consistent with Asp128 or Glu128 acting as a general acid to donate a proton to the phenolate leaving group in the phosphorylation step, and the carboxylate side chain plays a role as a general base to activate a nucleophilic water molecule in the dephosphorylation step. The presence of the general acid ensures productive partitioning toward phosphoenzyme formation. In the absence of the general acid, the nature of the transition-state for the phosphorylation step is sensitive to the pKa of the attacking active site thiol group and changes with the structure of the leaving group.

Aspartic Acid↗
PubMed1996

Specificity of coupling of muscarinic receptor isoforms to a novel chick inward-rectifying acetylcholine-sensitive K+ channel.

The G-protein-gated inward-rectifying K+ channel GIRK1 has been demonstrated in heart and brain. These tissues also both express the M2, M3, and M4, muscarinic acetylcholine receptors (mAChR) (Gadbut, A.P., and Galper, J.B. (1994),J. Biol. Chem. 269,25823-25829). Only the M2 mAChR has been demonstrated to couple to GIRK1 (Kubo, Y., Reuveny, E., Slesinger, P. A., Jan, Y. N., and Jan, L. Y. (1993) Nature 264, 802-806). In this study we determined the specificity of coupling of the M3 and M4 mAChR to a new GIRK1 cloned from a chick brain cDNA library. This clone codes for a 492-amino acid protein that is 93% identical to rat GIRK1 and is expressed in brain, atrium, and ventricle, but not skeletal muscle. In Xenopus laetis oocytes co-expression of GIRK1 with either the chick M2 or M4 mAChR gave carbamylcholine (10 microm)-stimulated K+ currents of 308 +/-26 nA and 298 +/-29 nA, respectively, which were both Ba2+- and pertussis toxin-sensitive. Activation of the M3 receptor produced 2382 +/-478 nA of current which was insensitive to Ba2+ and pertussis toxin, but was 85% inhabitable by the Cl channel blocker 5-nitro-2-(3-phenylpropylamino)benzoic acid (10-20 microm) consistent with coupling to an endogenous Ca2+-activated Cl- channel via a phosphatidylinositol-dependent mechanism. Co-expression of the cardiac inward rectifier CIR with chick M2 or M4 mAChR and GIRK1 increased currents more than 10-fold, but had no effect on specificity of coupling. These data demonstrate a new function for the M4 mAChR and a high degree of specificity for coupling of each receptor subtype to GIRK1.

Acetylcholine↗
PubMed1996

Determinants of substrate recognition in the protein-tyrosine phosphatase, PTP1.

Photoaffinity labeling has been used to identify amino acids involved in recognition of protein substrates by the protein-tyrosine phosphatase PTP1. The photoactive amino acid p-benzoylphenylalanine (Bpa) was incorporated into a phosphotyrosine-containing peptide derived from epidermal growth factor autophosphorylation site Tyr992 (EGFR988 998). This peptide photoinactivated PTP1 in a time- and concentration-dependent manner. Three lines of evidence indicate that the interaction between PTP1 and the photoaffinity label was specific: 1) photoinactivation was inhibited in the presence of a non-Bpa-containing peptide from EGFR Tyr992 in molar excess. 2) The photoaffinity label-containing phosphopeptide was rapidly dephosphorylated by PTP1 with kinetic constants similar to those of the non-Bpa-containing peptide under identical conditions. 3) After complete photoinactivation, the level of incorporation of radioactive photoaffinity label into PTP1 was approximately 0.9 mol of label/mol of enzyme, consistent with a 1:1 stoichiometry of photolabeling. Radiolabeled peptide was used to identify sites of cross-linking to PTP1. Bpa peptide-PTP1 was digested with trypsin, and radioactive fragments were purified by high performance liquid chromatography (HPLC) and analyzed by Edman sequencing. In two parallel experiments which were analyzed using different HPLC columns, a site in the alpha2 region of PTP1, most likely Ile23, was labeled by the Tyr992-derived peptide. The results are discussed in light of the crystal structure of human PTP1B and suggest that an additional mode of substrate recognition must exist for PTP1 catalysis.

Affinity Labels↗
PubMed1996

Modulation of K+ channel currents by serum amineoxidase in neurons.

The influence of bovine serum amineoxidase (SAO), a circulating copper-enzyme, on neuronal K+ channels is described. Bovine SAO enhanced K+ channel currents in N1E-115 neuroblastoma cells in a time-dependent manner. Unlike ceruloplasmin (another copper-protein, shown as depolarizing factor in neurons), SAO had no effect on resting potential of neurons. However, pretreatment of cells with SAO inhibited ceruloplasmin-induced membrane depolarization. Although ceruloplasmin alone inhibited K+ channel currents, it further enhanced K+ channel currents in the presence of SAO. Therefore, SAO may be another endogenous modulator of neuronal K+ channels with effect and mechanisms different from those of ceruloplasmin.

Amine Oxidase (Copper-Containing)↗
PubMed1996

Overlapping phenotypes of multidrug resistance among panels of human cancer-cell lines.

In addition to P-glycoprotein (Pgp), 2 proteins related to multidrug resistance (MDR) have recently been described. The Multidrug-Resistance-associated protein (MRP) is one of the ATP-binding-cassette (ABC) transporters. The Lung-Resistance Protein (LRP) is the major component of human vaults, which are newly described cellular organelles and thought to mediate intracellular transport processes. Using immunocytochemical methods, we have examined the expression of MRP and LRP among panels of human cancer-cell lines not selected for drug resistance which have been previously characterized for expression of Pgp, and in vitro response to a variety of anti-cancer drugs. Expression of MRP and LRP was observed in 47/55 (87%) and 46/59 (78%) cell lines, respectively. Statistically significant correlations were observed between expression of each of these 3 proteins and in vitro sensitivity to at least one drug classically associated with MDR. LRP showed the greatest individual predictive value, which also applied to several non-classical MDR drugs. Co-expression of 2-3 MDR-related proteins was observed in 64% of the lines and was, in general, associated with high relative levels of drug resistance. Previously identified "classic" MDR lines as well as "pan-resistant" lines concurrently expressed all 3 MDR-related proteins. Some highly drug-resistant cell lines without detectable MDRI/Pgp were found to express relatively high levels of MRP and LRP. The high prevalence of MRP and LRP expression observed in this large set of cell lines, which have not been subjected to laboratory drug selection, suggests that MDR mechanisms associated with these proteins may be widespread in human malignancies. Moreover, the overlapping of these more recently recognized MDR phenotypes with Pgp-type MDR results in a complex phenotype, the understanding of which may be of importance in the development of new drugs and design of clinical treatment protocols, particularly those seeking to employ strategies to reverse the MDR phenotype.

ATP-Binding Cassette Transporters↗
PubMed1996

Biochemical characterization of the human cyclin-dependent protein kinase activating kinase. Identification of p35 as a novel regulatory subunit.

The activation of cyclin-dependent protein kinases (Cdks) is dependent upon site-specific phosphorylation and dephosphorylation reactions, as well as positive and negative regulatory subunits. The human Cdk-activating protein kinase (Cak1) is itself a Cdc2-related cyclin-dependent protein kinase that associates with cyclin H. The present study utilized specific anti-Cak1 antibodies and immunoaffinity chromatography to identify additional Cak1-associated proteins and potential target substrates. Immunoprecipitation of metabolically labeled human osteosarcoma cells revealed a number of Cak1-associated proteins, including p95, p37 (cyclin H), and a 35-kDa protein that was further characterized herein. Microsequence analysis obtained after limited proteolysis revealed peptide fragments that are similar, but not identical to, human and yeast cyclins, thus identifying p35 as a cyclin-like regulatory subunit. The greatest sequence similarity of human p35 is with Mcs2, a yeast cyclin that is essential for cell cycle progression. Immunoaffinity chromatography performed under nondenaturing conditions afforded the isolation of enzymatically active Cak1 from cell lysates, enabling studies of kinase autophosphorylation and comparative substrate utilization. Immunoaffinity-purified Cak1 phosphorylated monomeric Cdc2 and Cdk2, but not Cdk4; the phosphorylation of both Cdc2 and Cdk2 were increased in the presence of recombinant cyclin A. These studies indicate that the Cak1 catalytic subunit, like Cdc2 and Cdk2, associates with multiple regulatory partners and suggests that subunit composition may be an important determinant of this multifunctional enzyme.

Amino Acid Sequence↗