硫代谢
中文名称
通路描述
硫是生命所必需的元素，有机硫化合物的代谢在全球硫循环中起着重要作用。硫存在于各种氧化态中，从硫酸盐中的 +6 态到硫化氢中的 -2 态。硫酸盐还原可以在消耗能量的同化途径和产生能量的异化途径中发生。同化途径在广泛的生物体中存在，产生含硫的还原化合物用于含硫氨基酸的生物合成，且不直接导致硫化氢的排泄。在异化途径中，它仅限于必需的厌氧细菌和古菌类群，硫酸盐（或硫）是呼吸链的末端电子受体，产生大量的无机硫化氢。两种途径都是从硫酸盐与 ATP 反应形成腺苷酰硫酸（APS）开始的。在同化途径 [MD:M00176] 中，APS 被转化为 3'-磷酸腺苷酰硫酸（PAPS），然后还原为亚硫酸盐，亚硫酸盐进一步还原为硫化氢，由同化亚硫酸盐还原酶催化。在异化途径 [MD:M00596] 中，APS 直接还原为亚硫酸盐，亚硫酸盐进一步还原为硫化氢，由异化亚硫酸盐还原酶催化。硫的氧化能力在细菌和古菌中相当广泛，包括光合自养生物和化能自养生物。SOX（硫氧化）系统 [MD:M00595] 是一个众所周知的硫氧化途径，存在于光合和非光合硫氧化细菌中。绿硫细菌和紫色硫细菌进行无氧光合作用，使用硫化氢和元素硫等还原硫化合物作为电子供体，以及硫代硫酸盐（在某些物种中，具有 SOX 系统的情况下），作为光自养生长的电子供体。在某些化能自养硫氧化菌（例如硫杆菌硝化杆菌）中，有建议异化硫还原酶在反向方向操作，形成从亚硫酸盐到 APS 再到硫酸盐的硫氧化途径。
英文描述
Sulfur is an essential element for life and the metabolism of organic sulfur compounds plays an important role in the global sulfur cycle. Sulfur occurs in various oxidation states ranging from +6 in sulfate to -2 in sulfide (H2S). Sulfate reduction can occur in both an energy consuming assimilatory pathway and an energy producing dissimilatory pathway. The assimilatory pathway, which is found in a wide range of organisms, produces reduced sulfur compounds for the biosynthesis of S-containing amino acids and does not lead to direct excretion of sulfide. In the dissimilatory pathway, which is restricted to obligatory anaerobic bacterial and archaeal lineages, sulfate (or sulfur) is the terminal electron acceptor of the respiratory chain producing large quantities of inorganic sulfide. Both pathways start from the activation of sulfate by reaction with ATP to form adenylyl sulfate (APS). In the assimilatory pathway [MD:M00176] APS is converted to 3'-phosphoadenylyl sulfate (PAPS) and then reduced to sulfite, and sulfite is further reduced to sulfide by the assimilatory sulfite reductase. In the dissimilatory pathway [MD:M00596] APS is directly reduced to sulfite, and sulfite is further reduced to sulfide by the dissimilatory sulfite reductase. The capacity for oxidation of sulfur is quite widespread among bacteria and archaea, comprising phototrophs and chemolithoautotrophs. The SOX (sulfur-oxidation) system [MD:M00595] is a well-known sulfur oxidation pathway and is found in both photosynthetic and non-photosynthetic sulfur-oxidizing bacteria. Green sulfur bacteria and purple sulfur bacteria carry out anoxygenic photosynthesis with reduced sulfur compounds such as sulfide and elemental sulfur, as well as thiosulfate (in some species with the SOX system), as the electron donor for photoautotrophic growth. In some chemolithoautotrophic sulfur oxidizers (such as Thiobacillus denitrificans), it has been suggested that dissimilatory sulfur reduction enzymes operate in the reverse direction, forming a sulfur oxidation pathway from sulfite to APS and then to sulfate.
所含基因
10 个基因