kilodalton

kilodalton
Name	kilodalton
Quantity	mass (molecular mass)
Units1	SI base units
Units2	dalton
Units3	gram

kilodalton

The kilodalton is a unit of molecular mass commonly used in biochemistry, molecular biology, and structural biology to express the mass of proteins, nucleic acids, and macromolecular complexes. It is a multiple of the dalton and is widely used alongside instruments, databases, and standards maintained by organizations and institutions involved in molecular science and metrology.

Definition and nomenclature

The kilodalton denotes one thousand daltons, where the dalton is defined in relation to the unified atomic mass standard adopted by the International Committee for Weights and Measures, the International Union of Pure and Applied Chemistry, the International Union of Pure and Applied Physics, and the National Institute of Standards and Technology. Nomenclature around the kilodalton appears in the literature of the European Molecular Biology Laboratory, the Max Planck Society, the Howard Hughes Medical Institute, the Cold Spring Harbor Laboratory, and in journals published by the American Chemical Society and the Nature Publishing Group. The unit symbol "kDa" is used in databases maintained by the Protein Data Bank, the UniProt Consortium, and the European Bioinformatics Institute as well as in methods described by the World Health Organization and the Food and Drug Administration.

History and adoption

Adoption of the dalton and kilodalton followed international standardization efforts involving the International Committee for Weights and Measures, the Comité International des Poids et Mesures, and scientific gatherings at institutions such as the Royal Society and the Max Planck Institute. Early protein chemistry reported masses in daltons in papers from laboratories at the University of Cambridge, the Massachusetts Institute of Technology, and the University of California, Berkeley before coordinated acceptance via meetings of the International Union of Pure and Applied Chemistry and the International Union of Pure and Applied Physics. The kilodalton became routine in textbooks from publishers like Oxford University Press, Cambridge University Press, and Springer Nature and in compendia from the National Institutes of Health and the European Commission.

Use in biochemistry and molecular biology

Researchers at the Max Planck Institute for Biochemistry, the Scripps Research Institute, the Fred Hutchinson Cancer Center, and the Karolinska Institutet report protein masses in kilodaltons when characterizing enzymes, antibodies, and complexes. Techniques such as SDS-PAGE, mass spectrometry developed at institutions like the University of Oxford, the California Institute of Technology, and the University of Tokyo produce results expressed in kDa in articles appearing in Cell (journal), Science (journal), Nature (journal), The Lancet, and publications of the American Association for the Advancement of Science. Databases including the Protein Data Bank, UniProt, and GenBank annotate sequences with molecular mass in kilodaltons, and standard protocols from the Cold Spring Harbor Laboratory Press and the European Molecular Biology Laboratory use kDa in reagent sheets from companies such as Sigma-Aldrich, Thermo Fisher Scientific, and Bio-Rad Laboratories.

Measurement and calculation

Mass spectrometry groups at the Max Planck Institute of Biochemistry, the Weizmann Institute of Science, and the Broad Institute calculate molecular masses in daltons and report kilodalton values in software packages like those from Agilent Technologies, Bruker, and Thermo Fisher Scientific. Gel electrophoresis markers produced by New England Biolabs and Sigma-Aldrich are labeled in kDa, and calibration against standards from the National Institute of Standards and Technology and the Physikalisch-Technische Bundesanstalt enables traceability. Computational resources at the European Bioinformatics Institute, the Wellcome Sanger Institute, and the J. Craig Venter Institute convert amino acid sequences into molecular mass using residue masses standardized by the International Union of Biochemistry and Molecular Biology.

Conversions and related units

One kilodalton equals 1,000 daltons; the dalton is defined relative to 1/12 the mass of a carbon-12 atom as ratified by the International Committee for Weights and Measures and discussed in reports from the International Bureau of Weights and Measures. Conversion to grams is applied in materials science and pharmacology literature from the European Medicines Agency and the U.S. Food and Drug Administration, while platforms like PubChem, ChEMBL, and DrugBank present molecular mass in daltons, kilodaltons, and grams per mole in accordance with recommendations by the International Union of Pure and Applied Chemistry.

Examples and typical ranges in biomolecules

Typical protein subunits characterized at the Protein Data Bank and in reviews from the Annual Review of Biochemistry span from small peptides (~1–5 kDa) to large enzymes (20–100 kDa) and megadalton assemblies studied at the European Synchrotron Radiation Facility and the European Molecular Biology Laboratory cryo-EM facilities. Antibodies reported by researchers at the Scripps Research Institute, Roche, and Genentech often measure ~150 kDa; histones cataloged in datasets from the Wellcome Trust Sanger Institute are around 11–15 kDa; ribosomal subunits described in work from the Max Planck Institute for Molecular Genetics and the MIT range from tens to hundreds of kilodaltons; viral capsid proteins published by teams at the Centers for Disease Control and Prevention and the Pasteur Institute vary widely across families.

Standards and metrology

Metrological traceability for dalton-based measurements involves the International Bureau of Weights and Measures, the National Institute of Standards and Technology, the Physikalisch-Technische Bundesanstalt, and interlaboratory comparisons coordinated by the International Organization for Standardization and the International Electrotechnical Commission. Guidelines from the World Health Organization, the European Directorate for the Quality of Medicines & HealthCare, and pharmacopeias such as the United States Pharmacopeia and the European Pharmacopoeia reference mass units including kilodaltons for characterization of biologics and vaccines developed by organizations like Pfizer, Moderna, AstraZeneca, and GSK.

Category:Units of mass