Sentence:  They were then centrifuged at 59780 rpm for 35 to 80 min at 20 ` C in a Spinco model E <WSD>ultracentrifuge</WSD> at a protein concentration of 1.00 to 1.25 % . 
Meaning of the word marked with <WSD> tags:  a high speed centrifuge used to determine the relative molecular masses of large molecules in high polymers and proteins