FTIR studies of organometalcarbonyl-tagged enzymes

Attachment of organometaltricarbonyl tags to enzymes is revealed by changes in the vibrational modes of the carbonyl groups. Shoulders on nu(sym)(CO) and nu(asym)(CO) bands in the FTIR spectrum of an organometallic tag derived from tricarbonyl[1-{(2,3,4,5-eta)-2,4-cyclohexadien-1-yl}pyridinium]iron(1+) hexafluorophosphate(1-)were detected on binding to enzymes (alpha-chymotrypsin, ribonuclease A, alkaline phosphatase and a triacylglycerol lipase). By comparison with tagging reactions between the tricarbonyliron moiety and model compounds, the new spectral features were attributed to an iron complex covalently bonded to the NH2 groups of the amino acid residues of the enzymes. FTIR spectroscopy was used to monitor deprotonation of tagged amino groups on the enzyme surface. Interactions between the organometalcarbonyl tag and other side-chain groups of the amino acid residues were also investigated. (C) 1997 Elsevier Science B.V.