CORRELATION OF X-RAY DEDUCED AND EXPERIMENTAL AMINO-ACID-SEQUENCES OFTRIMETHYLAMINE DEHYDROGENASE

The amino acid sequence of the iron-sulfur-flavoprotein, trimethylamin e dehydrogenase, isolated from the bacterium W3A1 has been deduced fro m the x-ray diffraction pattern obtained at 2.4-angstrom resolution. T his sequence has been compared to portions of the primary sequence der ived by gas-phase sequencing of isolated peptides obtained from cyanog en bromide and endoprotease Arg-C and Asp-N digestions of the purified enzyme. A consensus sequence has resulted and is comprised of 729 ami no acids with Ala at both NH2- and COOH-terminal positions. The consen sus sequence contains 13 cysteine residues. Approximately 80% of the s equence has been confirmed by direct sequencing with approximately 81% agreement with the x-ray deduced sequence. The calculated subunit mol ecular mass of the apoenzyme is 78,899 Da, in good agreement with publ ished values of approximately 83,000. The anomalous scattering map fro m the native protein has also been shown to provide accurate informati on about the positions of most of the weak anomalous scattering center s such as sulfur or phosphorus atoms and to complement x-ray or chemic al sequencing methods.