The situation is as follows. I have lysates of several cell types (TBS, freeze-thaw cycles, nothing special in buffer), determine the total protein content by Bradford, take 0.5 mg/ml of total protein for cleavage analysis of another purified protein, put it all on gel and see with Western if any cleavage occured.
So far so good, platelet and megakaryocyte lysates can be determined nicely, also on gel by CBB staining we can see that the matching of protein content worked.
But not erythrocytes. With them I get a huge overestimation of protein content, had to dilute the lysate 4000 times to get the readout within the standard curve. And that results in ~100-150x higher estimated protein content than other samples. And when I put the samples of gel, the lane of erythrocytes is empty. Tried to put 100x more concentrated erythrocyte sample on gel, got a big blue lane (i.e., too much protein). Of course, I can go on running gels with various dilutions of the erythrocyte sample till I have a lane that is comparable with other cell lysates but I'd like to be able to quantify it properly.
So the question is - does anybody know what could interfere with Bradford analysis in my erythrocyte sample. Anbody heard of haeme or haemoglobin giving problems in Bradford analysis? Any other suggestions how to quantify the total protein content in erythrocytes also would be welcome.