Hello Samima, 

    I also have faced this problem in my case when I was analyzing BSA interaction with Cu(II). I found HSA and BSA ITC thermogram different. So it is possible. You just make sure that there is no pH difference between protein and ligand solution and dialyze  protein sample if you are using commercial purchased protein. 

I will dialyze HSA and BSA in the same dialysis buffer and use the exactly same buffer during the whole experiment. If you still observe the same result, then it means the driven force of binding to BSA and HSA is different.  This paper (http://www.sciencedirect.com/science/article/pii/S0167483801002874) reports SDS binds to HSA and BSA differently.

Hi Samima,

it might well be that thermograms differ in between albumin species. It depends on the ligand of course. I suggest to have a glimpse at "All about albumin" from Theodore Peters Jr., if you did not yet ...

Basically, here and there people find astonishing differences in between albumin species, mainly by equilibrium dialysis, UV CD, DSC, Fluorescence, UV/VIS, EPR and NMR spectroscopy. From the amino acid sequence it is obvious that both proteins are not equivalent, but differences mainly comprise slight deviations in dissociation constants KD or in number of binding sites N for a specific ligand. Observing a complete different nature in binding thermodynamics is strange, maybe you should measure temperature dependent ITC and construct a Van´t Hoff plot from KD, then you might be able to further refine your findings.

Here are some interesting papers in this regard:

Gantchev (1990): http://dx.doi.org/10.1016/0167-4838(90)90046-I

Akdogan (2012): http://dx.doi.org/10.1371/journal.pone.0045681

Maruthamuthu (1988): DOI: 10.1007/BF02841127

I hope this could help a bit.

kindly,

Jörg

Thank you Sir for your answer..Yess i got my solution.its the temperature which gave me the result..by keeping increasing the temperature the endothermic gives exothermic graph