title: Photothermal studies of pH induced unfolding of apomyoglobin.
abstract: Conformational dynamic and enthalpy changes associated with pH induced unfolding of apomyoglobin were studied using photoacoustic calorimetry and photothermal beam deflection methods. The transition between the native state and the I intermediate was induced by a nanosecond pH jump from o-nitrobenzaldehyde photolysis. Deconvolution of photoacoustic waves indicates two kinetic processes. The fast phase (T < 50 ns) is characterized by a volume expansion of 8.8 ml mol(-1). This process is followed by a volume contraction of about -22 ml mol(-1) (tau approximately 500 ns). Photothermal beam deflection measurements do not reveal any volume changes on the time scale between approximately 100 micros and 5 ms. We associate the volume contraction with structural changes occurring during the transition between the native state and the I intermediate. The lack of any processes on the ms time scale may indicate the absence of structural events involving larger conformational changes of apomyoglobin after the pH jump.
mesh_terms: D000162:Acoustics; D000818:Animals; D001059:Apoproteins / Q000737:chemistry* / Q000378:metabolism; D002942:Circular Dichroism; D006736:Horses; D009206:Myocardium / Q000737:chemistry; D009211:Myoglobin / Q000737:chemistry* / Q000378:metabolism; D010782:Photolysis; D011487:Protein Conformation / Q000528:radiation effects; D011489:Protein Denaturation / Q000528:radiation effects; D017510:Protein Folding; D013696:Temperature; D013816:Thermodynamics
chemical_list: D001059:Apoproteins; D009211:Myoglobin; C010857:apomyoglobin