Nickel-sequestering renal glycoprotein

Abstract

Kidney is the target organ where nickel is accumulated and subsequently excreted in the urine after an intraperitoneal administration of 63NiCl2 in rats. The radioactive nickel is found mostly bound to a low molecular weight protein in kidney, which was isolated, purified, and partially characterized in this study. Homogeneity of this protein was determined by polyacrylamide gel electrophoresis. Amino acid analysis showed the presence of high amounts of glycine and proline and low amounts of phenylalanine, tyrosine, hydroxyproline, and hydroxylysine. The protein was found to be a glycoprotein with a carbohydrate content of 10% (wt/wt). Preliminary carbohydrate analysis showed that this glycoprotein is a high mannose-type containing mannose, galactose/glucose, and glucosamine. On the basis of the amino acid and carbohydrate analyses, the molecular weight of the glycoprotein is about 15,000-16,000. In vitro addition of nickel to the kidney cytosol also showed the presence of this protein. The protein appeared not to be affected or altered in its nickel-binding capacity by intraperitoneal or intravenous administration of actinomycin D, indicating it to be a noninducible protein. The glycoprotein demonstrated many characteristics of renal basement membrane. It is proposed that this protein is either a part of the renal basement membrane or is a part of the procollagen in the process of its conversion to collagen of the renal basement protein. The protein has a high affinity for nickel. It also may possess a similar binding affinity for other metals as well and may constitute a natural process of handling toxic levels of metals to be excreted.