@article {4726,
	title = {Methanol-induced conformations of myoglobin at pH 4.0},
	journal = {Biochemistry},
	volume = {39},
	number = {47},
	year = {2000},
	note = {ISI Document Delivery No.: 378UETimes Cited: 62Cited Reference Count: 78},
	month = {Nov},
	pages = {14702-14710},
	type = {Article},
	abstract = {The equilibrium methanol-induced conformation changes of holomyoglobin (hMb) at pH 4.0 have been studied by circular dichroism, tryptophan fluorescence, and Soret band absorption and by electrospray ionization mass spectrometry (ESI-MS). Optical spectra show the following: (1) In 35-40\% (v/v) methanol/water, the native-like secondary structure remains, the tertiary structure is lost, the heme protein interactions are decreased, and a folding intermediate is formed. (2) In 50\% methanol, heme is lost from the protein, and there is a small decrease in helicity together with a loss of tertiary structure. (3) At > 60\% methanol, the helicity increases and the apoprotein goes into a helical denatured state. The conformations are also probed by the charge states produced in ESI-MS and by hydrogen/deuterium (H/D) exchange with mass measurement by ESI-MS. At 0-30\% methanol, native hMb produces relatively low charge states (9(+)-13(+)) in ESI-MS and exchanges relatively few hydrogens. In 35-40\% methanol, at which an intermediate is formed, there is a bimodal distribution of hMb ions with both low (9(+)-13(+)) and high (14(+)-23(+)) charge states and also a high charge state distribution (12(+)-26(+)) of apomyoglobin (aMb) ions. Low and high charge states of hMb and a high charge state of aMb all show the same H/D exchange rate, indicating that an unfolded hMb intermediate interconverts between folded hMb and unfolded aMb. The charge state distribution for the unfolded hMb intermediate observed here is similar to that of the recently reported transient intermediate formed during the acid denaturation of hMb. At 50\% alcohol the protein produces predominantly high charge states of aMb ions and shows H/D exchange rates close to those of the acid-denatured protein. H/D exchange of the helical denatured protein at alcohol concentrations >60\%, at which high charge states of aMb are produced, shows that the protein structure is more protected than at similar to 50\% methanol.},
	keywords = {AMIDE HYDROGEN-EXCHANGE, APOMYOGLOBIN, BETA-LACTOGLOBULIN, CYTOCHROME-C, ELECTROSPRAY-IONIZATION, FOLDING INTERMEDIATE, IONIZATION MASS-SPECTROMETRY, MOLTEN GLOBULE INTERMEDIATE, SPERM-WHALE, STRUCTURAL-CHARACTERIZATION, X-RAY-SCATTERING},
	isbn = {0006-2960},
	url = {<Go to ISI>://000165602400040},
	author = {Babu, K. R. and Douglas, D. J.}
}
@article {4030,
	title = {Acid-induced denaturation of myoglobin studied by time-resolved electrospray ionization mass spectrometry},
	journal = {Biochemistry},
	volume = {36},
	number = {21},
	year = {1997},
	note = {ISI Document Delivery No.: XB321Times Cited: 74Cited Reference Count: 43},
	month = {May},
	pages = {6448-6454},
	type = {Article},
	abstract = {The acid-induced denaturation of holo-myoglobin (hMb) following a pH-jump from 6.5 to 3.2 has been studied by electrospray ionization (ESI) mass spectrometry in combination with a continuous flow mixing technique (time-resolved ESI MS). Different protein conformations are detected by the different charge state distributions that they generate during ESI. The changes in intensity of the peaks in the mass spectrum as a function of time can be described by two exponential lifetimes of 0.38 +/- 0.06 s and 6.1 +/- 0.5 s, respectively. The acid-induced denaturation of hMb was also studied in stopped-flow experiments by monitoring changes in the Soret absorption. The lifetimes measured by this method are in good agreement with those obtained by time-resolved ESI MS. The shorter lifetime is associated with the formation of a transient intermediate which shows the mass of the intact heme-protein complex but leads to the formation of much higher charge states during ESI than native hMb at pH 6.5. This form of hMb has an absorption spectrum similar to that of the native protein, indicating a relatively unperturbed chromophore environment inside the heme binding pocket. The intermediate can thus be characterized as an unfolded form of hMb with essentially intact heme-protein interactions. The longer of the two lifetimes is associated with the formation of a product which has a blue-shifted absorption spectrum with a much lower maximum absorption coefficient than observed for native hMb. In the ESI mass spectrum, this product appears as the apoprotein with high charge states which indicates the disruption of the native heme-protein interactions and a considerable degree of unfolding compared to native apo-myoglobin. The mechanism of acid-induced denaturation of hMb, therefore, appears to follow the sequence (heme protein)(native) {\textendash}> (heme-protein)(unfolded) {\textendash}> heme + (protein)(unfolded).},
	keywords = {APOMYOGLOBIN, HEME-PROTEINS, INTERMEDIATE, IONS, LOW PH, METMYOGLOBIN, PROBING CONFORMATIONAL-CHANGES, RESOLUTION, SPERM WHALE, STABILITY},
	isbn = {0006-2960},
	url = {<Go to ISI>://A1997XB32100022},
	author = {Konermann, L. and Rosell, F. I. and Mauk, A. G. and Douglas, D. J.}
}
