Sentence:  Treatment of all the sera with sweet clover <WSD>proteins</WSD> greatly reduced nonspecific fluorescence , especially when the treated conjugate was diluted to 1 : 2 with 0.85 % saline . 
Meaning of the word marked with <WSD> tags:  any of a large group of nitrogenous organic compounds that are essential constituents of living cells; consist of polymers of amino acids; essential in the diet of animals for growth and for repair of tissues; can be obtained from meat and eggs and milk and legumes