The first step of the mineralisation of fosfomycin by R. huakuii PMY1 is hydrolytic ring opening with the formation of (1R,2R)-1,2-dihydroxypropylphosphonic acid. This phosphonic acid and its three stereoisomers were synthesised by chemical means and tested as their ammonium salts for mineralisation as evidenced by release of Pi. Only the (1R,2R)-isomer was degraded. A number of salts of phosphonic acids such as (±)-1,2-epoxybutyl-, (±)-1,2-dihydroxyethyl-, 2-oxopropyl-, (S)-2-hydroxypropyl-, (±)-1-hydroxypropyl- and (±)-1-hydroxy-2-oxopropylphosphonic acid were synthesised chemically, but none supported growth. In vitro C–P bond cleavage activity was however detected with the last phosphonic acid. A mechanism involving phosphite had to be discarded as it could not be used as a phosphorus source. R. huakuii PMY1 grew well on (R)- and (S)-lactic acid and hydroxyacetone, but less well on propionic acid and not on acetone or (R)- and (±)-1,2-propanediol. The Pi released from (1R,2R)-1,2-dihydroxypropylphosphonic acid labelled with one oxygen-18 in the PO3H2group did not stay long enough in the cells to allow complete exchange of 18O for 16O by enzymic turnover.
R. huakuii
PMY1 矿化
磷霉素的第一步是
水解开环,形成 (1R,2R)-
1,2-二羟基丙基膦酸。通过
化学方法合成了这种
膦酸及其三种立体异构体,并测试了它们作为
铵盐的矿化作用,Pi 的释放证明了这一点。只有 (1R,2R)-异构体被降解。
化学合成了一些
膦酸盐,如(±)-1,2-环
氧丁基-、(±)-1,2-二羟乙基-、2-
氧代丙基-、(S)-2-羟基丙基-、(±)-1-羟基丙基-和(±)-1-羟基-2-
氧代
丙基膦酸,但没有一种能支持生长。不过,在最后一种
膦酸中检测到了体外 C-P 键裂解活性。由于
亚磷酸不能用作
磷源,因此必须放弃涉及
亚磷酸的机制。R. huakuii
PMY1 在(R)-和(S)-
乳酸和
羟基丙酮上生长良好,但在
丙酸上生长较差,在
丙酮或(R)-和(±)-
1,2-丙二醇上生长不良。从(1R,2R)-
1,2-二羟基丙基膦酸中释放出的 Pi 在 PO3H2 组中标记了一个
氧-18,但在细胞中停留的时间不够长,无法通过酶的转换将 18O 完全交换为 16O。