白色念珠菌摄取生物素的机制研究

STUDIES ON THE MECHANISMS OF BIOTIN TRANSPORT BY CANDIDA ALBICANS

本文进一步实验显示处于生物素饥饿状态的白色念珠菌摄取生物素具可饱合性和特异性。从饱合曲线测算出主动摄入生物素的半数最大初速率（１／２Ｖｍａｘ）所需生物素浓度，即Ｋｍ值为０７９±０１１（平均数±标准差，ｎ＝８）；叠氮钠（５ｍＭｏｌ／Ｌ）处理后，其Ｋｍ值增到２３９±０６４μｍＭｏｌ／Ｌ（平均数±标准差，ｎ＝３）。生物素之结构同源分子，如脱硫生物素、生物胞素、甲基酯生物素和对硝基苯酯生物素等竞争性抑制其主动摄取生物素，但是２亚氨基生物素却完全无抑制作用。在生物素摄入充足的白色念珠菌（在含２０ｎＭｏｌ／Ｌ生物素的培养基中生长），生物素主要通过简单的弥散方式进入菌体内。由于血清中的生物素含量在ｐＭｏｌ／Ｌ到几个ｎＭｏｌ／Ｌ之间，白色念珠菌在体内可能通过主动摄取生物素机制满足其营养代谢需求。

C.albicans can be propagated in Littman's medium(LM),a simple and fully defined glucose-salts solution,only if biotin is added.Because maximal growth rates require approximately 100 pMol/L biotin,C.albicans grown in LM that contains 20 pMol/L biotin are relatively biotin-deficient.Biotin uptake by biotindeficient C. albicans was energy-dependent,saturable and specific.Structural analogs of biotin,including desthiobiotin,biocytin,and two esterified biotin were competitive inhibitors of active biotin transport,but 2-iminobiotin was noninhibitory.The Km for active biotin transport by biotin-deficient C. albicans was 0 79±0 11 (mean±S.E.M.,n=8).Sodium azide (5mMol/L),but not sodium cyanide,potently inhibited biotin transport by biotin-deficient C.albicans.The Km for biotin transport by azide-treated biotin-deficient C. albicans was increased to 2 39±0 64μMol/L(mean±S.E.M.,n=3)。When C.albicans was grown in LM that contained 20 nMol/L biotin,the resulting biotin-suffieient organisms took up biotin principally by facilitated diffusion and showed little active transport.Because concentrations of biotin in serum are in the low range of nMol/L,C.albicans probably satisfies its requirenment for biotin in vivo principally via active transport.This study may provide some scientific basis for developing new antifungal strategies.