Molecular localization of zinc in rat milk and neonatal intestine

The molecular localization of zinc in rat milk and pup intestine was determined by gel chromatography. Commerical gels were found to give low recoveries of zinc and also caused anomalous elution patterns. Treatment of the gel with sodium borohydride corrected these problems. With treated gels, all of the zinc in rat milk eluted with high molecular weight proteins (MW greater than or equal to 30,000). In neonatal intestine, zinc eluted in two major peaks with molecular weights 30,000 and 6,000-8,000, respectively. However, incubating intestinal homogenates at 37 degrees for 30 minutes produced a redistribution of zinc with a new major low molecular weight (less than or equal to 1,500) peak. These results demonstrate the importance of sample preparation and chromatographic conditions when studying trace element ligands and also suggest that rat milk is not analogous to human milk in regard to zinc binding.