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This Article Full Text (PDF) All Versions of this Article: jas.2008-1341v1 87/14_suppl/E85    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Hill, G. M. Articles by Link, J. E. Search for Related Content PubMed PubMed Citation Articles by Hill, G. M. Articles by Link, J. E.

Transporters in the absorption and utilization of Zn and Cu

Animal Science Department, Michigan State University, East Lansing, MI 48824

hillgre{at}msu.edu

Abstract

Before the discovery and elucidation of transporters, mammals were thought to co-transport Cu or Zn as an anionic complex, such as binding with an amino acid as a chelate or a receptor such as transferrin. In 1995, the first Zn mammalian transporter gene, ZnT1, was identified. However, it is now thought that two protein families are involved in Zn transport. The ZnT family reduces intracellular Zn by aiding in efflux from the cell or promoting the influx into intracellular vesicles. The mechanism of ZnT transport against a Zn concentration gradient is unknown; however, only the ZnT1 transporter appears to be located at the plasma membrane. It has been shown to respond in tissues in a variety of manners to Zn reduction and supplementation. Our laboratory has found ZnT1 and metallothionein to work in concert during pharmacological Zn supplementation. The second protein family, Zip proteins, provides Zn transport from extracellular fluid or intracellular vesicles into the cytoplasm and has not been identified in a livestock species. Like Zn, no good indicator of status has been identified for Cu. However, the recent identification of Cu transporters and chaperones give researchers the opportunity to understand the regulation of Cu-trafficking where the proteins are modified by post-translational mechanisms. Two Cu transporters, Ctr1 and Ctr3, mediate high affinity Cu uptake. A small cytoplasmic protein, MURR1, has been identified in human hepatic tissue, but its role in Cu metabolism is unknown. The discovery of Cu chaperones that are involved in facilitating Cu absorption into proteins may provide an excellent status indicator. It has been shown that the Cu chaperone for Cu/Zn superoxide dismutase (CCS) is increased in tissue of Cu deficient rats induced when moderately high Zn diets were fed. We have recently found CCS in the young pig. Other Cu chaperone proteins that have been identified are COX17 and Atox1. As with CCS, they are involved in making Cu available to apo-enzymes inside the cell. It is essential that these new molecular findings be utilized to evaluate bioavailability and nutritional needs of Cu and Zn in livestock.

Key Words: copper • transport proteins • zinc