Thermodynamic analysis of hydration in human serum heme-albumin.
Ferric human serum heme-albumin (heme-HSA) shows a peculiar nuclear magnetic relaxation dispersion (NMRD) behavior that allows to investigate structural and functional properties. Here, we report a thermodynamic analysis of NMRD profiles of heme-HSA between 20 and 60 degrees C to characterize its hydration. NMRD profiles, all showing two Lorentzian dispersions at 0.3 and 60 MHz, were analyzed in terms of modulation of the zero field splitting tensor for the S=5/2 manifold. Values of correlation times for tensor fluctuation (tau(v)) and chemical exchange of water molecules (tau(M)) show the expected temperature dependence, with activation enthalpies of -1.94 and -2.46+/-0.2 kJ mol(-1), respectively. The cluster of water molecules located in the close proximity of the heme is progressively reduced in size by increasing the temperature, with DeltaH=68+/-28 kJ mol(-1) and DeltaS=200+/-80 J mol(-1) K(-1). These results highlight the role of the water solvent in heme-HSA structure-function relationships.
Baroni
Simona
S
Invento S.r.l., "Companies Incubator" of the University of Torino, Via Nizza 52, I-10126 Torino, Italy.
Pariani
Giorgio
G
Fanali
Gabriella
G
Longo
Dario
D
Ascenzi
Paolo
P
Aime
Silvio
S
Fasano
Mauro
M
D006418:Heme / Q000737:chemistry*; D006358:Hot Temperature; D006801:Humans; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D012709:Serum Albumin / Q000737:chemistry*; D013329:Structure-Activity Relationship; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
D012709:Serum Albumin; D014867:Water; D006418:Heme