Watanabe F, Nakano Y, Tamura Y, Yamanaka H
Laboratory of Nutrition and Food Science, Hagoromo-gekuen College, Osaka, Japan.
Biochim Biophys Acta. 1991 Sep 2;1075(1):36-41. doi: 10.1016/0304-4165(91)90071-n.
To elucidate vitamin B12 (cobalamin) metabolism in green algae, Chlamydomonas reinhardtii was labeled with radioactive cobalamin for 4 days. The Chlamydomonas cells did not require cobalamin for growth, but nevertheless took up and accumulated exogenous cobalamin. The level of the accumulated cobalamin reached a maximum (about 20 fmol/10(6) cells) at day 1 of the cell growth. The cobalamin accumulated by the 4-day cells was partly converted to the coenzymes (5'-deoxyadenosylcobalamin, 20.7% and methylcobalamin, 4.8%). The cells contained NADH- and NADPH-linked aquacobalamin reductases (35.9 and 31.5 nmol/min per mg protein, respectively) involved in the synthesis of the coenzymes. Most of the accumulated cobalamin was associated with two heat-labile macromolecules; the coenzymes synthesized were recovered in the macromolecular fraction with a molecular weight of 230,000, while non-coenzyme forms (cyanocobalamin and hydroxocobalamin) predominated in that with a molecular weight of 40,000. Evidence for de novo biosynthesis of cobalamin was also obtained in the alga, indicating that it has both ability to synthesize cobalamin and take up the exogenous vitamin.
为阐明绿藻莱茵衣藻中维生素B12（钴胺素）的代谢情况，用放射性钴胺素标记莱茵衣藻4天。莱茵衣藻细胞生长不需要钴胺素，但仍能摄取并积累外源钴胺素。在细胞生长第1天，积累的钴胺素水平达到最高（约20飞摩尔/10⁶个细胞）。4天龄细胞积累的钴胺素部分转化为辅酶（5'-脱氧腺苷钴胺素，20.7%；甲基钴胺素，4.8%）。细胞含有参与辅酶合成的NADH-和NADPH-连接的水钴胺素还原酶（分别为每毫克蛋白质35.9和31.5纳摩尔/分钟）。积累的大部分钴胺素与两种热不稳定大分子相关；合成的辅酶在分子量为230,000的大分子组分中回收，而非辅酶形式（氰钴胺素和羟钴胺素）在分子量为40,000的组分中占主导。在该藻类中还获得了钴胺素从头生物合成的证据，表明它既有合成钴胺素的能力，又能摄取外源维生素。
