= J. Stenflo
{c}
<J. Stenflo> coauthored the 1974 work identifying <gamma-carboxyglutamic acid> in <prothrombin>, connecting <Vitamin K> dependence with a specific chemical modification of a clotting protein. The study isolated a four-residue peptide from the calcium-binding amino-terminal region and found mobility that ordinary amino-acid composition did not explain.<Vitamin K dependent modifications of glutamic acid residues in prothrombin by J. Stenflo and others>[Abstract: peptide residues6–9 and anomalous electrophoretic mobility]{ref}
<Nuclear magnetic resonance> and <mass spectrometry> identified two modified glutamic-acid residues in that peptide. The result supplied a chemical identity for the anomaly, rather than treating an altered migration pattern alone as a complete explanation.<Vitamin K dependent modifications of glutamic acid residues in prothrombin by J. Stenflo and others>[Abstract: proton NMR, mass spectrometry and two gamma-carboxyglutamic-acid residues]{ref}
An additional carboxyl group changes a side chain's chemical possibilities, including its interactions with ions. This makes post-synthesis chemistry biologically significant: two protein preparations with the same genetically specified sequence can differ in modifications and function. The finding helped connect a nutritional requirement, a measurable molecular difference and the behavior of a <calcium>-binding <protein>, while preserving the distinction between a chemical observation and a physiological inference.
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