About 30% of boar seminal plasma nitrogen is maximally precipitated at room temperature by 6 to 10 mm zinc in citrate solution at pH 8. A rise in the total nitrogen precipitated by 1 to 6 mm zinc is accompanied by a fall in the haemagglutinin titre of the supernatant fluid. At 6 mm zinc addition, 95% of the haemagglutinin is precipitated, but much of this is recoverable by resolution of the zinc precipitate. Protein profile studies by gel-filtration chromatography of the zinc precipitate solution reveals a mixture of proteins, some of which are not by themselves zinc-precipitable.

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