Farquharson J, Adams J F
Am J Clin Nutr. 1977 Oct;30(10):1617-22. doi: 10.1093/ajcn/30.10.1617.
During determinations of the forms of vitamin B12 in foods and human tissues several samples yielded a growth zone on bioautography which was distinct from those due to methylcobalamin, adenosylcobalamin, hydroxocobalamin, or cyanocobalamin. The material responsible for this growth zone was identified as sulfitocobalamin and the mechanisms in its formation from hydroxocobalamin involve absence of light and the presence of bisulphite ions derived from atmospheric sulfur dioxide or indigenous sulfite ions. The formation of sulfitocobalamin during the extraction of cobalamins from foods and tissues can be prevented by reception and homogenization of the material in an ammonia buffer instead of water; the hydroxocobalamin is then converted to ammonia cobalamin, which is more resistant to attack by (bi)sulfite ions. The conversion of hydroxo(aquo)cobalamin to sulfitocobalamin in the dark can be rapid, and materials for analysis should be placed in the ammonia buffer before darkroom work is begun. The rapid conversion of hydroxo(aquo)cobalamin to sulfitocobalamin in the dark raises the possibility that hydroxocobalamin in foods may be converted to the less well absorbed sulfitocobalamin in the upper gastrointestinal tract.
在测定食品和人体组织中维生素B12的形式时，有几个样品在生物自显影中产生了一个生长区，该生长区与甲基钴胺素、腺苷钴胺素、羟钴胺素或氰钴胺素产生的生长区不同。造成这个生长区的物质被鉴定为亚硫酸钴胺素，其由羟钴胺素形成的机制涉及无光以及存在源自大气二氧化硫或内源性亚硫酸根离子的亚硫酸氢根离子。从食品和组织中提取钴胺素时，通过在氨缓冲液而非水中接收和匀浆材料，可以防止亚硫酸钴胺素的形成；然后羟钴胺素会转化为氨钴胺素，其更能抵抗（亚）硫酸根离子的攻击。在黑暗中，羟（水合）钴胺素快速转化为亚硫酸钴胺素，因此在暗室工作开始前，分析材料应置于氨缓冲液中。黑暗中羟（水合）钴胺素快速转化为亚硫酸钴胺素增加了食品中的羟钴胺素可能在上消化道转化为吸收性较差的亚硫酸钴胺素的可能性。
