25kDa

25 kDa (kilodaltons) is a unit of molecular mass used to describe the size of proteins and other macromolecules. One dalton is defined as one twelfth of the mass of a carbon-12 atom, and 1 kDa equals 1000 daltons. A protein with an approximate mass of 25 kDa is typically in the range of about 220 to 230 amino acids, though the exact length depends on amino acid composition and any post-translational modifications.

In laboratory practice, 25 kDa is a common reference point in techniques such as SDS-PAGE, where gel mobility correlates with molecular weight, and in mass spectrometry and chromatography where masses are reported in kilodaltons. Proteins near this size may consist of a single compact domain or multiple smaller domains.

Post-translational modifications—including phosphorylation, glycosylation, and lipidation—can increase the apparent molecular mass beyond the unmodified value. Proteolytic processing can alternatively produce fragments around 25 kDa or smaller. When annotating genes, predicted protein masses are calculated from sequence and compared with experimental masses to assess expression, processing, and potential modifications.

There is no single protein universally designated as '25kDa'; rather, 25 kDa is a range descriptor used across studies to categorize proteins, enzymes, and other macromolecules by their approximate mass.