Isoform
A slightly different version of a peptide or protein that arises from variations in gene expression, alternative splicing, or post-translational modification. Different isoforms of the same molecule may have distinct biological activities — for example, growth hormone has multiple naturally occurring isoforms.
Technical Context
Multiple isoforms arise from alternative mRNA splicing, post-translational modifications, or allelic variation. Growth hormone has a predominant 22 kDa isoform (approximately 90% of circulating GH) and a 20 kDa isoform (approximately 10%) from alternative splicing of the same gene. These isoforms have different receptor binding properties and biological activities. Recombinant somatropin is the 22 kDa isoform. IGF-1 exists in multiple isoforms due to alternative splicing and differential glycosylation. Understanding isoform biology is important because drug development targets specific isoforms, and analytical methods must distinguish between them during quality control.