Structural characterization of myo-inositol monophosphatase from bovine brain by secondary structure prediction, fluorescence, circular dichroism and Raman spectroscopy.

Structural aspects of myo-inositol monophosphatase were examined by spectroscopic techniques and empirical prediction methods. The enzyme belongs to the alpha/beta class of proteins, with approx. 33% alpha-helix and 29% beta-sheet, as shown by circular dichroism (CD), Raman spectroscopy and prediction based on the amino-acid sequence. The Raman spectrum also suggests that the three tryptophan residues in myo-inositol monophosphatase are not exposed to solvent. This was confirmed by a blue shift of 25 nm in the fluorescence emission spectrum, as compared to tryptophan in water, and by quenching studies with acrylamide. The enzyme shows a transition temperature of 87 degrees C for the CD signal at 222 nm. This remarkable heat stability is not due to the presence of disulfide bonds, since both the Raman spectrum and chemical modification studies clearly indicate that all six cysteine residues are in the reduced state.