title: Conformational properties of human and rat apolipoprotein A-IV.
abstract: Apolipoprotein A-IV has been isolated from four sources: human and rat lymph and plasma. Conformational properties of the rat and human apoA-IV in solution and denaturation changes induced by guanidine hydrochloride (Gnd X HCl) were studied using circular dichroic and fluorescence spectroscopy, and analytical sedimentation equilibrium ultracentrifugation. We have shown that both rat and human apoA-IV have similar secondary structure with negative maxima in the circular dichroic spectra at 222 nm and 207 nm. Furthermore, we have found no significant difference in the alpha-helical content of the apoA-IV from rat plasma (33%), rat lymph (37%), human plasma (35%), or human lymph (35%). Our denaturation studies with Gnd X HCl demonstrated reversibility and the fact that each apoA-IV had a tendency to self-associate in solution and the self-association could be disrupted by low concentrations of Gnd X HCl (less than or equal to 0.4 M). Unfolding of the secondary structure of each apoA-IV occurred at higher concentrations of Gnd X HCl (midpoint less than or equal to 1.0 M). The apparent free energy of denaturation of the four apoA-IV proteins calculated from changes in the circular dichroic spectra upon addition of increasing concentrations of Gnd X HCl varied in a range from 3.0 to 4.2 kcal/mol. The fluorescence experiments revealed that apoA-IV from all sources had a maximum fluorescence emission at 342.5 nm, which shifted to the red region upon addition of increasing concentrations of Gnd X HCl.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001054:Apolipoproteins A / Q000032:analysis*; D002942:Circular Dichroism; D006801:Humans; D008297:Male; D008433:Mathematics; D011487:Protein Conformation; D051381:Rats; D011919:Rats, Inbred Strains; D013045:Species Specificity; D013050:Spectrometry, Fluorescence
chemical_list: D000596:Amino Acids; D001054:Apolipoproteins A; C022205:apolipoprotein A-IV