kilodaltons

Kilodalton is a unit of molecular mass equal to one thousand daltons (Da). The dalton is defined as one twelfth of the mass of a carbon-12 atom, and is approximately 1.660539066 × 10^-27 kilograms. Therefore, one kilodalton (kDa) equals 1000 Da and is about 1.66 × 10^-24 kilograms. In biochemistry and molecular biology, kilodaltons are commonly used to express the masses of proteins, nucleic acids, and their complexes, because these biomolecules typically fall within the kilodalton range.

The dalton and the atomic mass unit (amu) are effectively the same scale, with 1 Da ≈ 1 g/mol. The kilodalton is simply a thousand times larger, so 1 kDa ≈ 1000 g/mol. The symbol for the unit is kDa. In practice, the term kilodalton is used interchangeably with the abbreviation kDa when describing molecular weights.

Commonly cited examples illustrate the range of kDa values for biomolecules: insulin is about 5.8 kDa, myoglobin around 17 kDa, albumin roughly 66 kDa, and an IgG antibody about 150 kDa. Large enzyme complexes and multi-subunit assemblies can reach several hundred kilodaltons or more, and some ribosomal subunits and viral particles approach the megadalton scale.

Measurement methods for molecular mass include mass spectrometry (such as MALDI-TOF or ESI-MS) for precise weight determinations, and techniques like size-exclusion chromatography or analytical ultracentrifugation for approximate masses and hydrodynamic properties. Kilodaltons describe mass, not length; they should not be confused with kilobases, which measure genetic length.