1
|
Gu L, Hu TX. A simplified non-reduced peptide mapping method with faster and efficient enzymatic digestion for characterization of native disulfide bonds in monoclonal and bispecific antibodies. J Pharm Biomed Anal 2024; 250:116400. [PMID: 39126811 DOI: 10.1016/j.jpba.2024.116400] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2024] [Revised: 08/03/2024] [Accepted: 08/04/2024] [Indexed: 08/12/2024]
Abstract
Development of monoclonal and bispecific antibody-based protein therapeutics requires detailed characterization of native disulfide linkages, which is commonly achieved through peptide mapping under non-reducing conditions followed by liquid chromatography-mass spectrometry (LC-MS) analysis. One major challenge of this method is incomplete protein digestion due to insufficient denaturation of antibodies under non-reducing conditions. For a long time, researchers have explored various strategies with the aim of efficiently digesting antibody drugs when the disulfide bonds remain intact, but few could achieve this by using a simple and generic approach with well controlled disulfide scrambling artifacts. Here, we report a simple method for fast and efficient mapping of native disulfides of monoclonal and bispecific antibody-based protein therapeutics. The method was optimized to achieve optimal digestion efficiency by denaturing proteins with 8 M urea plus 0-1.25 M guanidine-HCl at elevated temperature (50 °C), followed by two-step digestion with trypsin/Lys-C mix using a one-pot reaction. The only parameter that needs to be optimized for different proteins is the concentration of guanidine-HCl present. This simplified sample preparation eliminated buffer exchange and can be completed within three hours. By using this new method, all native disulfide bonds were confirmed for these monoclonal and bispecific antibodies with high confidence. When compared with a commercial kit utilizing low-pH digestion condition, the new method demonstrated higher digestion efficiency and shorter sample preparation time. These results suggest this new one-pot-two-step digestion method is suitable for the characterization of antibody disulfide bonds, particularly for those antibodies with digestion-resistant domains under typical digestion conditions.
Collapse
Affiliation(s)
- Liqing Gu
- Biologics Analytical Science, Incyte Corporation, 1801 Augustine Cut-off, Wilmington, DE 19803, USA.
| | - Tiger X Hu
- Biologics Analytical Science, Incyte Corporation, 1801 Augustine Cut-off, Wilmington, DE 19803, USA
| |
Collapse
|
2
|
Chaturvedi S, Bawake S, Sharma N. Recent advancements in disulfide bridge characterization: Insights from mass spectrometry. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2024; 38:e9713. [PMID: 38361473 DOI: 10.1002/rcm.9713] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2023] [Revised: 01/13/2024] [Accepted: 01/14/2024] [Indexed: 02/17/2024]
Abstract
RATIONALE Disulfide bridges (DSB) play an important role in stabilizing three-dimensional structures of biopharmaceuticals, single purified proteins, and various cyclic peptide drugs that contain disulfide in their structures. Incorrect cross-linking known as DSB scrambling results in misfolded structures that can be inactive, immunogenic, and susceptible to aggregation. Very few articles have been published on the experimental annotation of DSBs in proteins and cyclic peptide drugs. Accurate characterization of the disulfide bond is essential for understanding protein confirmation. METHODS Characterizing DSBs using mass spectrometry (MS) involves the chemical and enzymatic digestion of samples to obtain smaller peptide fragments, in both reduced and nonreduced forms. Subsequently, these samples are analyzed using MS to locate the DSB, either through interpretation or by employing various software tools. RESULTS The main challenge in DSB analysis methods using sample preparation is to obtain a sample solution in which nonnative DSBs are not formed due to high pH, temperature, and presence of free sulfhydryl groups. Formation of nonnative DSBs can lead to erroneous annotation of disulfide bond. Sample preparation techniques, fragmentation methods for DSB analysis, and contemporary approaches for DSB mapping using this fragmentation were discussed. CONCLUSIONS This review presents the latest advancement in MS-based characterization; also a critical perspective is presented for further annotation of DSBs using MS, primarily for single purified proteins or peptides that are densely connected and rich in cysteine. Despite significant breakthroughs resulting from advancements in MS, the analysis of disulfide bonds is not straightforward; it necessitates expertise in sample preparation and interpretation.
Collapse
Affiliation(s)
- Sachin Chaturvedi
- Department of Pharmaceutical Analysis, National Institute of Pharmaceutical Education and Research-Ahmedabad (Ministry of Chemicals and Fertilizers, Government of India), NIPER Ahmedabad Opposite Air force Station Palaj, Gandhinagar, Gujarat, India
| | - Sanket Bawake
- Department of Pharmaceutical Analysis, National Institute of Pharmaceutical Education and Research-Ahmedabad (Ministry of Chemicals and Fertilizers, Government of India), NIPER Ahmedabad Opposite Air force Station Palaj, Gandhinagar, Gujarat, India
| | - Nitish Sharma
- Department of Pharmaceutical Analysis, National Institute of Pharmaceutical Education and Research-Ahmedabad (Ministry of Chemicals and Fertilizers, Government of India), NIPER Ahmedabad Opposite Air force Station Palaj, Gandhinagar, Gujarat, India
| |
Collapse
|
3
|
Jagannath DK, Valiyaparambil A, Viswanath VK, Hurakadli MA, Kamariah N, Jafer AC, Patole C, Pradhan S, Kumar N, Lakshminarasimhan A. Refolding and characterization of a diabody against Pfs25, a vaccine candidate of Plasmodium falciparum. Anal Biochem 2022; 655:114830. [DOI: 10.1016/j.ab.2022.114830] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2022] [Revised: 03/28/2022] [Accepted: 07/20/2022] [Indexed: 11/28/2022]
|
4
|
Nupur N, Rathore AS. Elucidating chemical and disulfide heterogeneities in rituximab using reduced and non-reduced peptide mapping. J Sep Sci 2022; 45:2887-2900. [PMID: 35670633 DOI: 10.1002/jssc.202200290] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2022] [Revised: 06/03/2022] [Accepted: 06/03/2022] [Indexed: 11/07/2022]
Abstract
Peptide mapping by liquid chromatography-mass spectrometry is the gold standard to characterize post-translational modifications and disulfide bonds. The structural integrity, heterogeneity, and quality of biotherapeutic proteins are evaluated via reduced and non-reduced peptide mapping methods. However, non-enzymatic artifacts are often induced during sample preparation when alkaline pH conditions are used. To minimize these artifacts, methods using various acidic pH conditions have been developed by multiple researchers. However, these may lead to missed and non-specific cleavages during the analysis. In this study, improved reduced and non-reduced peptide mapping method has been proposed to characterize endogenous chemical modifications and native disulfide bonds of monoclonal antibody -based products. Solubilization has been carried out at acidic pH conditions under high temperature, followed by the addition of tris (2-carboxyethyl) phosphine as a reducing agent and a low alkylating agent. It was observed that the non-enzymatic post-translational modifications and non-native disulfide scrambled peptides significantly reduced under trypsin plus Lys-C digestion conditions at acidic pH as compared to the traditional methods. The results demonstrate that the proposed peptide mapping method using trypsin plus Lys-C could identify and quantify various chemical and disulfide heterogeneities with minimal artifacts. This article is protected by copyright. All rights reserved.
Collapse
Affiliation(s)
- Neh Nupur
- Department of Chemical Engineering, IIT Delhi, Hauz Khas, New Delhi, 110016, India.,DBT Center of Excellence for Biopharmaceutical Technology, IIT Delhi, Hauz Khas, New Delhi, 110016, India
| | - Anurag S Rathore
- Department of Chemical Engineering, IIT Delhi, Hauz Khas, New Delhi, 110016, India.,DBT Center of Excellence for Biopharmaceutical Technology, IIT Delhi, Hauz Khas, New Delhi, 110016, India
| |
Collapse
|
5
|
Nie S, Greer T, Huang X, Zheng X, Li N. Development of a simple non-reduced peptide mapping method that prevents disulfide scrambling of mAbs without affecting tryptic enzyme activity. J Pharm Biomed Anal 2021; 209:114541. [PMID: 34954467 DOI: 10.1016/j.jpba.2021.114541] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2021] [Revised: 12/16/2021] [Accepted: 12/17/2021] [Indexed: 11/27/2022]
Abstract
Non-reduced peptide mapping by liquid chromatography-mass spectrometry (LC-MS) analysis is a commonly used method for disulfide linkage characterization to assess structural integrity and quality of therapeutic monoclonal antibodies (mAbs). However, disulfide scrambling artifacts induced during sample preparation are often observed when basic pH and high temperatures are used during denaturation and digestion. To minimize disulfide scrambling artifacts, methods using various acidic pH conditions have been developed by multiple groups. However, lower pH conditions increase missed and non-specific cleavages, which complicates disulfide bond analysis because the majority of enzymes used in protein characterization are most efficient at alkaline pH. Here, we developed a non-reduced peptide mapping method for mAb characterization that minimizes disulfide scrambling at basic pH by adding an oxidizing agent, cystamine, and a low concentration of iodoacetamide (IAA) alkylating agent. Two human IgG1 mAbs, one with kappa light chain and another one with lambda light chain, were used as model proteins to develop and optimize the method. Using this novel method, disulfide scrambled peptides related to light chain-heavy chain (LC-HC) inter-disulfide disruption were significantly reduced with high reproducibility compared to conventional methods. Results demonstrated that the cystamine-added method is robust and minimizes disulfide scrambling artifacts produced during sample preparation.
Collapse
Affiliation(s)
- Song Nie
- Analytical Chemistry, Regeneron Pharmaceuticals Inc., 777 Old Saw Mill River Road, Tarrytown, NY 10591-6707, United States
| | - Tyler Greer
- Analytical Chemistry, Regeneron Pharmaceuticals Inc., 777 Old Saw Mill River Road, Tarrytown, NY 10591-6707, United States
| | - Xiaoxiao Huang
- Analytical Chemistry, Regeneron Pharmaceuticals Inc., 777 Old Saw Mill River Road, Tarrytown, NY 10591-6707, United States
| | - Xiaojing Zheng
- Analytical Chemistry, Regeneron Pharmaceuticals Inc., 777 Old Saw Mill River Road, Tarrytown, NY 10591-6707, United States.
| | - Ning Li
- Analytical Chemistry, Regeneron Pharmaceuticals Inc., 777 Old Saw Mill River Road, Tarrytown, NY 10591-6707, United States
| |
Collapse
|
6
|
Park HM, Winton VJ, Drader JJ, Manalili Wheeler S, Lazar GA, Kelleher NL, Liu Y, Tran JC, Compton PD. Novel Interface for High-Throughput Analysis of Biotherapeutics by Electrospray Mass Spectrometry. Anal Chem 2020; 92:2186-2193. [PMID: 31880920 PMCID: PMC7008517 DOI: 10.1021/acs.analchem.9b04826] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
With the rapid rise of therapeutic antibodies and antibody-drug conjugates, significant investments have been made in developing workflows that utilize mass spectrometry to detect these intact molecules, the large fragments generated by their selective digestion, and the peptides generated by traditional proteomics workflows. The resultant data is used to gain insight into a wide range of parameters, including primary sequence, disulfide bonding, glycosylation patterns, biotransformation, and more. However, many of the technologies utilized to couple these workflows to mass spectrometers have significant limitations that force nonoptimal modifications to upstream sample preparation steps, limit the throughput of high-volume workflows, and prevent the harmonization of diverse experiments onto a single hardware platform. Here, we describe a new analytical platform that enables direct and high-throughput coupling to electrospray ionization mass spectrometry. The SampleStream platform is compatible with both native and denaturing electrospray, operates with a throughput of up to 15 s/sample, provides extensive concentration of dilute samples, and affords similar sensitivity to comparable liquid chromatographic methods.
Collapse
Affiliation(s)
- Hae-Min Park
- Proteomics Center of Excellence, Northwestern University, 2170 Campus Drive, Evanston, Illinois 60208, United States
| | - Valerie J. Winton
- Proteomics Center of Excellence, Northwestern University, 2170 Campus Drive, Evanston, Illinois 60208, United States
| | - Jared J. Drader
- Integrated Protein Technologies, Inc., 2170 Campus Drive, Evanston, IL 60208, United States
| | - Sheri Manalili Wheeler
- Integrated Protein Technologies, Inc., 2170 Campus Drive, Evanston, IL 60208, United States
| | - Greg A. Lazar
- Genentech, Inc., 1 DNA Way, South San Francisco, California 94080, United States
| | - Neil L. Kelleher
- Proteomics Center of Excellence, Northwestern University, 2170 Campus Drive, Evanston, Illinois 60208, United States
- Integrated Protein Technologies, Inc., 2170 Campus Drive, Evanston, IL 60208, United States
| | - Yichin Liu
- Genentech, Inc., 1 DNA Way, South San Francisco, California 94080, United States
| | - John C. Tran
- Genentech, Inc., 1 DNA Way, South San Francisco, California 94080, United States
| | - Philip D. Compton
- Proteomics Center of Excellence, Northwestern University, 2170 Campus Drive, Evanston, Illinois 60208, United States
- Integrated Protein Technologies, Inc., 2170 Campus Drive, Evanston, IL 60208, United States
| |
Collapse
|
7
|
Liu-Shin LPY, Fung A, Malhotra A, Ratnaswamy G. Evidence of disulfide bond scrambling during production of an antibody-drug conjugate. MAbs 2018; 10:1190-1199. [PMID: 30339473 DOI: 10.1080/19420862.2018.1521128] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Antibody-drug conjugates (ADCs) that are formed using thiol-maleimide chemistry are commonly produced by reactions that occur at or above neutral pHs. Alkaline environments can promote disulfide bond scrambling, and may result in the reconfiguration of interchain disulfide bonds in IgG antibodies, particularly in the IgG2 and IgG4 subclasses. IgG2-A and IgG2-B antibodies generated under basic conditions yielded ADCs with comparable average drug-to-antibody ratios and conjugate distributions. In contrast, the antibody disulfide configuration affected the distribution of ADCs generated under acidic conditions. The similarities of the ADCs derived from alkaline reactions were attributed to the scrambling of interchain disulfide bonds during the partial reduction step, where conversion of the IgG2-A isoform to the IgG2-B isoform was favored.
Collapse
Affiliation(s)
- Lily Pei-Yao Liu-Shin
- a Analytical and Formulation Development , Agensys, Inc., an affiliate of Astellas, Inc , Santa Monica , CA , USA.,b Department of Biochemistry and Molecular Biology , University of Miami Miller School of Medicine , Miami , FL , USA
| | - Adam Fung
- a Analytical and Formulation Development , Agensys, Inc., an affiliate of Astellas, Inc , Santa Monica , CA , USA
| | - Arun Malhotra
- b Department of Biochemistry and Molecular Biology , University of Miami Miller School of Medicine , Miami , FL , USA
| | - Gayathri Ratnaswamy
- a Analytical and Formulation Development , Agensys, Inc., an affiliate of Astellas, Inc , Santa Monica , CA , USA
| |
Collapse
|
8
|
Lakbub JC, Shipman JT, Desaire H. Recent mass spectrometry-based techniques and considerations for disulfide bond characterization in proteins. Anal Bioanal Chem 2017; 410:2467-2484. [PMID: 29256076 DOI: 10.1007/s00216-017-0772-1] [Citation(s) in RCA: 59] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2017] [Revised: 11/09/2017] [Accepted: 11/17/2017] [Indexed: 12/21/2022]
Abstract
Disulfide bonds are important structural moieties of proteins: they ensure proper folding, provide stability, and ensure proper function. With the increasing use of proteins for biotherapeutics, particularly monoclonal antibodies, which are highly disulfide bonded, it is now important to confirm the correct disulfide bond connectivity and to verify the presence, or absence, of disulfide bond variants in the protein therapeutics. These studies help to ensure safety and efficacy. Hence, disulfide bonds are among the critical quality attributes of proteins that have to be monitored closely during the development of biotherapeutics. However, disulfide bond analysis is challenging because of the complexity of the biomolecules. Mass spectrometry (MS) has been the go-to analytical tool for the characterization of such complex biomolecules, and several methods have been reported to meet the challenging task of mapping disulfide bonds in proteins. In this review, we describe the relevant, recent MS-based techniques and provide important considerations needed for efficient disulfide bond analysis in proteins. The review focuses on methods for proper sample preparation, fragmentation techniques for disulfide bond analysis, recent disulfide bond mapping methods based on the fragmentation techniques, and automated algorithms designed for rapid analysis of disulfide bonds from liquid chromatography-MS/MS data. Researchers involved in method development for protein characterization can use the information herein to facilitate development of new MS-based methods for protein disulfide bond analysis. In addition, individuals characterizing biotherapeutics, especially by disulfide bond mapping in antibodies, can use this review to choose the best strategies for disulfide bond assignment of their biologic products. Graphical Abstract This review, describing characterization methods for disulfide bonds in proteins, focuses on three critical components: sample preparation, mass spectrometry data, and software tools.
Collapse
Affiliation(s)
- Jude C Lakbub
- Ralph N. Adams Institute for Bioanalytical Chemistry, Department of Chemistry, University of Kansas, 1251 Wescoe Hall Dr, Lawrence, KS, 66045, USA
| | - Joshua T Shipman
- Ralph N. Adams Institute for Bioanalytical Chemistry, Department of Chemistry, University of Kansas, 1251 Wescoe Hall Dr, Lawrence, KS, 66045, USA
| | - Heather Desaire
- Ralph N. Adams Institute for Bioanalytical Chemistry, Department of Chemistry, University of Kansas, 1251 Wescoe Hall Dr, Lawrence, KS, 66045, USA.
| |
Collapse
|
9
|
Wang Y, Li X, Liu YH, Richardson D, Li H, Shameem M, Yang X. Simultaneous monitoring of oxidation, deamidation, isomerization, and glycosylation of monoclonal antibodies by liquid chromatography-mass spectrometry method with ultrafast tryptic digestion. MAbs 2016; 8:1477-1486. [PMID: 27598507 DOI: 10.1080/19420862.2016.1226715] [Citation(s) in RCA: 60] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Monoclonal antibodies are subjected to a wide variety of post-translational modifications (PTMs) that cause structural heterogeneity. Characterization and control of these modifications or quality attributes are critical to ensure antibody quality and to define any potential effects on the ultimate safety and potency of antibody therapeutics. The biopharmaceutical industry currently uses numerous tools to analyze these quality attributes individually, which requires substantial time and resources. Here, we report a simple and ultrafast bottom-up liquid chromatography-mass spectrometry (uLC-MS) method with 5 min tryptic digestion to simultaneously analyze multiple modifications, including oxidation, deamidation, isomerization, glycation, glycosylation, and N-terminal pyro-glutamate formation, which can occur during antibody production in mammalian cell culture, during purification and/or on storage. Compared to commonly used preparation procedures, this uLC-MS method eliminates assay artifacts of falsely-increased Met oxidation, Asp isomerization, and Asn deamidation, a problem associated with long digestion times in conventional LC-MS methods. This simple, low artifact multi-attribute uLC-MS method can be used to quickly and accurately analyze samples at any stage of antibody drug development, in particular for clone and media selection during cell culture development.
Collapse
Affiliation(s)
- Yi Wang
- a Bioprocess Development, Merck Research Laboratories, Merck & Co., Inc. , Kenilworth , NJ , USA
| | - Xiaojuan Li
- a Bioprocess Development, Merck Research Laboratories, Merck & Co., Inc. , Kenilworth , NJ , USA
| | - Yan-Hui Liu
- a Bioprocess Development, Merck Research Laboratories, Merck & Co., Inc. , Kenilworth , NJ , USA
| | - Daisy Richardson
- a Bioprocess Development, Merck Research Laboratories, Merck & Co., Inc. , Kenilworth , NJ , USA
| | - Huijuan Li
- a Bioprocess Development, Merck Research Laboratories, Merck & Co., Inc. , Kenilworth , NJ , USA
| | - Mohammed Shameem
- a Bioprocess Development, Merck Research Laboratories, Merck & Co., Inc. , Kenilworth , NJ , USA
| | - Xiaoyu Yang
- a Bioprocess Development, Merck Research Laboratories, Merck & Co., Inc. , Kenilworth , NJ , USA
| |
Collapse
|
10
|
High throughput peptide mapping method for analysis of site specific monoclonal antibody oxidation. J Chromatogr A 2016; 1460:51-60. [DOI: 10.1016/j.chroma.2016.06.085] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2016] [Revised: 05/24/2016] [Accepted: 06/30/2016] [Indexed: 02/06/2023]
|
11
|
Cheng Y, Chen Y, Yu C. Fast and Efficient non-reduced Lys-C digest using pressure cycling technology for antibody disulfide mapping by LC-MS. J Pharm Biomed Anal 2016; 129:203-209. [PMID: 27429370 DOI: 10.1016/j.jpba.2016.07.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2016] [Revised: 07/01/2016] [Accepted: 07/02/2016] [Indexed: 10/21/2022]
Abstract
Conventional sample preparation for antibody disulfide mapping often requires relatively long digestion time (from several hours to overnight) and relatively high endoproteinase concentration. These conditions are typically necessitated by the fact that antibody molecules are not sufficiently denatured under non-reduced conditions and chaotropic agents are used during digestion to achieve optimal denaturation. Disulfide scrambling can occur as artifacts of digestion as proteins are incubated for extended periods, often at neutral to slightly alkaline pH conditions. Shortening digestion time and lowering the pH during digestion frequently result in incomplete peptide cleavages or variable recoveries. Here, we report the development of a fast and efficient non-reduced Lys-C digestion method based on pressure cycling technology (PCT) and its application in determining disulfide-linkages in monoclonal antibodies (mAbs). Conditions were optimized to ensure complete digestion of the mAb with minimal sample preparation-related disulfide scrambling. The PCT-based method was able to generate up to 10-fold signal increase for some disulfide peptides in a 1h Lys-C digestion compared to the conventional bench-top digestion method. As a result of the shorter digestion time, disulfide scrambling that is seen as a major assay artifact of the conventional method was reduced to less than 0.05% in tested molecules. The results show that the PCT-based method offers fast digestion in a shorter time for all the mAbs tested.
Collapse
Affiliation(s)
- Ying Cheng
- Protein Analytical Chemistry, Genentech Inc., 1 DNA Way, South San Francisco, CA 94080, USA.
| | - Yonghong Chen
- Protein Analytical Chemistry, Genentech Inc., 1 DNA Way, South San Francisco, CA 94080, USA
| | - Christopher Yu
- Protein Analytical Chemistry, Genentech Inc., 1 DNA Way, South San Francisco, CA 94080, USA
| |
Collapse
|