kilodaltoni

Kilodalton is a unit of mass commonly used in biochemistry and molecular biology to express the molecular mass of biomolecules, especially proteins and nucleic acids. It equals 1000 daltons, where the dalton (Da) is defined as one twelfth of the mass of a carbon-12 atom. By convention, 1 Da is equal to 1 gram per mole, so 1 kilodalton (kDa) equals 1000 Da and also 1000 g per mole (which is 1 kilogram per mole).

In practice, the kilodalton is convenient because the masses of many biomolecules fall within the range of a few to several hundred kilodaltons. For example, lysozyme is about 14.3 kDa, bovine serum albumin around 66 kDa, and the prokaryotic ribosome lies in the megadalton range (approximately 2.5 MDa, i.e., about 2500 kDa).

Kilodaltons are widely used in experimental reporting and data analysis. Mass spectrometry methods such as MALDI-TOF and electrospray (ESI) routinely yield molecular masses in Da or kDa. Gel-based and chromatographic techniques, including SDS-PAGE and size-exclusion chromatography, describe molecular size using kDa markers for calibration and interpretation. The kilodalton remains the standard unit for reporting the masses of most proteins and many other macromolecules in biological research.