The effects of dietary Ca and vitamin, D_3 on the Cd accumulation in the liver and the kidney were observed and discussed in relation with the responses to the intestinal Ca transport and vitamin D dependent calcium binding protein (CaBP). 1. Ca transport in rat duodenum was significantly increased by vitamin D_3, especially in rats raised on low P diet. However, this effect was reduced in Cd-exposed rats. 2. ^<45>Ca binding activity of the smaller CaBP (PIII), which was found predominantly in the duodenum and jejunum was increased by low P diet. However, in Cd-exposed rats, ^<45>Ca binding activity was suppressed significantly. On the other hand, the larger CaBP (PII) found mainly in jejunum and ileum showed a good response to vitamin D_3, too, but not influenced by dietary P and Cd levels as the smaller CaBP. 3. Renal Cd accumulation was influenced by neither dietary P nor vitamin D_3. However, hapatic Cd accumulation was significantly decreased in vitamin D_3 repleted rat, although it was not influenced by dietary P. These results suggest that dietary P modulates the inhibitory effect of Cd on intestinal vitamin D-stimulated Ca transport, presumably through the inhibition of Ca binding to the smaller CaBP(PIII). But Cd accumulation in the liver was decreased in vitamin D repleted groups, presumably, vitamin D dependent CaBP acts as the barrier in the Cd-exposed rats.

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Studies were carried out on the preparation of a vitamin B_<12>-bound adsorbent suitable for purifying CH_3-B_<12>-dependent enzyme by affinity chromatography. The results obtained were as follows: 1) Several B_<12> derivatives modified in the upper ligand were synthesized to examine their affinities with apo-methionine synthetase from Escherichia coli. Carboxypropyl-B_<12> was chosen as the ligand of the adsorbent, judging from its sufficient affinity to the apo-enzyme, the activation of the inactive enzyme complex by photolysis and slight non-specific interaction of the upper ligand moiety with apoenzyme. 2) Aminobutyl group was bound to Sepharose as the spacer, since spacer should not interact with the enzyme protein non-specifically and must keep an appropriate distance between the ligand and the carrier. 3) The ligand and the spacer-carrier chosen as above were coupled with a water-soluble carbodiimide to get an affinity adsorbent having the structure of Sepharose-(CH_2)_4-NHCO-(CH_2)_3-B_<12>. 4) B_<12>-dependent methionine synthetase from E. coli was highly purified with a good yield in only one step by the affinity chromatography on this B_<12>-bound Sepharose.

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