= R. E. Humbel
{c}
<R. E. Humbel> coauthored experimental work identifying the chemical structure of human insulin-like growth factors with <E. Rinderknecht>. Their 1978 study determined the complete sequence of serum-derived <insulin-like growth factor 1>: a single chain of seventy <amino acid residues> connected by three <disulfide bonds>.<The amino acid sequence of human insulin-like growth factor I and its structural homology with proinsulin by E. Rinderknecht and R. E. Humbel>[Abstract: complete sequence, chain length and disulfide bridges]{ref}
The comparison with <proinsulin> connected a biological activity to a molecular relationship. Corresponding regions resembled the insulin chains, while an intervening connecting segment remained in the growth factor. Conserved residues were compatible with a related folded structure; sequence similarity was evidence for that inference, not an atomic structure determination.<The amino acid sequence of human insulin-like growth factor I and its structural homology with proinsulin by E. Rinderknecht and R. E. Humbel>[Abstract: insulin-chain correspondence, connecting segment and structural interpretation]{ref}
This research illustrates why a bioassay and sequence analysis complement one another. Two preparations can produce similar responses without containing identical <proteins>. Establishing residue order and covalent connections provides an independent way to distinguish related signaling molecules.
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