Aspartate aminotransferase (AAT) enzyme was being purified from pigs heart. Tissues were homogenated and cells were eliminated with gel filtration. Nucleic acids were precipitated with polyethylenimine and extract1 was received with volume 2dm3. Then 50microLitres of this extract1 were added to 3cm3 buffer and optical density was measured at 280nm (1cm light path) and the value of it was 1,7. How should I count the amount of protein in extract1?

What do you know about using Beer's law?  I have a feeling that you will only be able to obtain an approximate answer, but it is better than nothing.

58 minutes ago, BabcockHall said:

What do you know about using Beer's law?

"do not overdo it with alcohol because you will have a hangover"..

 

To a rough approximation, when one has 1 mg/mL of protein, the absorbance at 280 nm will be 1 AU.  Obviously this depends on the protein.