The temperature-dependent opalescence caused by the presence of a zinc-precipitable protein (ZPP) in boar seminal plasma has been shown to be pH-dependent.
The considerable pH increase to which boar seminal plasma is subject on exposure to air is attributed to loss of CO2 from a system with a notable paucity of titratable groups in the physiological range pH 7 to 9. This markedly affects the temperature-dependent opalescence.
The ZPP has been purified and the temperature-dependent opalescence of this material can be demonstrated only within a narrow range of zinc concentration in the absence of other possible ligands present in whole seminal plasma.
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