Task: Named Entity Recognition
Input (English):  Using purified proteins , we have prepared a five - protein heterocomplex assembly system consisting of two proteins essential for heterocomplex assembly - hsp90 and hsp70 - and three proteins that act as co - chaperones to enhance assembly - Hop , hsp40 , p23 [ Morishima , Y . , Kanelakis , K . C . , Silverstein , A . M . , Dittmar , K . D . , Estrada , L . , and Pratt , W . B . ( 2000 ) J . Biol . Chem . 275 , 6894 - 6900 ] .
Output (English): purified proteins