Nickel-sequestering renal glycoprotein.

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Abstract
Kidney is the target organ where Ni is accumulated and subsequently excreted in the urine after an i.p. administration of 63NiCl2 in rats. The radioactive Ni is found mostly bound to a low MW protein in kidney, which was isolated, purified and partially characterized. 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 hydroxylsine. The protein was 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 MW of the glycoprotein is about 15,000-16,000. In vitro addition of Ni to the kidney cytosol also showed the presence of this protein. The protein appeared not to be affected on altered in its Ni-binding capacity by i.p. or i.v. 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 Ni. 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.