Estimation and Interpretation on Plasma Zinc Fractions

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Abstract
After intestinal absorption by humans, Zn is concentrated in the liver and there redistributed between 3 main plasma fractions: a tightly bound Zn-a2 macroglobulin complex, a more loosely bound Zn-albumin complex and low molecular weight complexes of Zn. The latter 2 fractions may be in equilibrium and provide the main transport of Zn to the cells. Procedures designed to estimate the Zn content of each of these fractions are described. Selective protein precipitation with polyethylene glycol 6000 (PEG) is used to separate the high molecular weight a2 macroglobulin from albumin and low molecular weight complexes. The Zn concentration of the supernatant is then determined by atomic absorption spectrophotometry (AAS). The Zn content of the low molecular weight complexes is determined by ultrafiltration of the plasma through a cellulose nitrate membrane (MW cut off 10,000), followed by estimation of the Zn concentration of the ultrafiltrate (200 .mu.l) by a modified AAS method. Total plasma Zn concentration is also determined by AAS. The Zn content of each of the 3 plasma fractions can then be obtained.

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