Separation by hybrid isoelectric focusing of normal human plasma transthyretin (prealbumin) and a variant with a methionine for valine substitution associated with familial amyloidotic polyneuropathy

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Abstract
The human plasma transthyretin (TTR, prealbumin) variant TTR(Met30) has been separated from normal TTR(Val30) by double one‐dimensional electrophoresis using polyacrylamide gel electrophoresis followed by hybrid isoelectric focusing. The procedure appears to be appropriate for identification by the screening of patients with familial amyloidotic polyneuropathy of Portuguese type I. This is the second example to support the recently expressed hypothesis (Altland et al., Electrophoresis 1986, 7, 251–259) that substitutions of electrically neutral amino acids (e. g. methionine for valine at position 30) in a polypeptide chain (e. g. the TTR monomer) may be detected by isoelectric focusing under denaturing conditions (e. g. hybrid isoelectric focusing in the presence of 8 M urea, 50 mM dithiothreitol) when the exchange is close to a charged amino acid (e. g. histidine at position 31, pI (TTR) = 5.7, pKa (His) = 6.0).