@article{oai:sapmed.repo.nii.ac.jp:00014888,
 author = {北村, 公一 and 大黒, 浩},
 issue = {6},
 journal = {札幌医学雑誌 = The Sapporo medical journal, The Sapporo medical journal},
 month = {Dec},
 note = {It has been established that the long-lived proteins of the mammalian eye lens slowly accumulate D-aspartyl（D-Asp） and L-isoaspartyl （L-Isoasp） residues as an apparent consequence of aging. Protein carboxyl-o-methyltransferase （PCMT） [EC.2.1.1.24], which is widely distributed in mammalian tissues, has been found to selectively methylate the β-carboxyl group of the uncommon D-Asp and L-Isoasp residues in proteins. Considering these findings, it has been proposed that PCMT plays a role in the repair or degradation of the abnormal amino acid residues that accumulate in aged proteins. PCMT has been detected in the bovine eye lens, however, the enzyme in the lens has not been characterized in detail. In the present study, we studied the properties and structure of the enzyme in the bovine lens. 1. Type II of PCMT （PCMT-II） was purified more than 13,000-fold from the cytosol of bovine lens. The apparent molecular weight of the PCMT-II on SDS-PAGE was approximately 27,000. The activity of type I of PCMT, which was not absorbed on DEAE-cellulose, was extremely low in the bovine lens. 2. The PCMT-II from the lens was composed of at least two molecular species, II a and II b, which were separated by a Mono-Q column. The pI was 5.8 for IIa and 5.6 for IIb. The two molecular species were found to have similar Km and Vmax values. The optimum pH of IIa activity ?was about 6.5, IIb activity showed a clearly lower pH optimum of less than 6.0. 3. The relative rates between PCMT-IIa and IIb activities were very similar with five proteins as methyl accepting substrates. Crystallin, the main protein constituent in the lens, gave the largest methylating rate of any protein examined here. 4. Antibody raised against PCMT-II from bovine lens crossreacted with PCMT-I and II from bovine brain, and PCMT from human erythrocyte. 5. The amino acid compositions of PCMT-IIa and IIb from bovine lens and PCMT-II from bovine brain were very similar. The HPLC profiles of lysylendopeptidase digests of PCMT-IIa and IIb from bovine lens and PCMT-II from bovine brain were also very similar, suggesting that similar seqences are present among these three enzymes. 6. The amino acid sequence in each peak of the lysylendopeptidase digests of PCMT-II a from bovine lens was almost identical with that of PCMT-I from bovine brain and PCMT-II from human and bovine erythrocytes reported by other investigators. These results suggest that PCMT-I and II of various organs from different mammalian species may have nearly identical structures. Therefore, differences in pI and pH optimum between PCMT-IIa and IIb from bovine lens may be due to the structural modification of the enzyme.},
 pages = {601--614},
 title = {ウシ水晶体におけるProtein Carboxyl-o-Methyltransferaseに関する研究},
 volume = {59},
 year = {1990}
}