The mode of occurrence of carotene and vitamin A in human blood plasma

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Abstract
Only small amts. of carotene and vit. A are extracted from citrated plasma by shaking with ether; lowering the pH increases extraction, with max. at pH 4-5; shaking with ether denatures and precipitates the protein. The presence of ethanol increases the extractability of carotene from plasma; bile salts decrease the amt. of carotene and vit. A extracted by ether. Half saturation of plasma with (NH4)2SO4 causes no precipitation of carotene or vit. A; f or complete saturation precipitates these substances with albumin from which they are not readily extracted by ether. Freezing plasma at [long dash]25[degree] in contact with ether increases in the amt. of carotene and vit. A extracted. Carotene in aqueous colloidal soln. added to normal plasma becomes unextractable, but not if the plasma was first shaken with ether. The evidence is held to indicate the existence of compounds of carotene and vit. A with protein.

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