ABSTRACT
Virginiamycin M
1
(VM
1
), produced by
Streptomyces virginiae
, is a polyunsaturated macrocyclic lactone antibiotic belonging to the virginiamycin A group.
S. virginiae
possesses an activity which stereospecifically reduces a 16-carbonyl group of VM
1
, resulting in antibiotically inactive 16
R
-dihydroVM
1
. The corresponding VM
1
reductase was purified to homogeneity from crude extracts of
S. virginiae
in five steps, with 5,650-fold purification and 23% overall yield. The N-terminal amino acid sequence was determined to be MAIKLVIA. The purified enzyme showed an apparent
M
r
of 73,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and an
M
r
of 280,000 by native molecular sieve high-performance liquid chromatography, indicating the tetrameric nature of the native enzyme. NADPH served as a coenzyme for the reduction, with a
K
m
value of 0.13 mM, but NADH did not support the reaction, even at a concentration of 5 mM, indicating the NADPH-specific nature of the enzyme. The
K
m
for VM
1
was determined to be 1.5 mM in the presence of 2 mM NADPH. In the reverse reaction, only 16
R
-dihydroVM
1
, not the 16
S
-epimer, served as a substrate, with a less than 0.1% overall reaction rate compared to that of the forward reaction, confirming that the VM
1
reductase participates solely in VM
1
inactivation in vivo.
摘要
由 Streptomyces virginiae 生产的多不饱和大环内酯类抗生素,属于维吉纳霉素 A 组,其中维吉纳霉素 M1(VM1)是一种。 S. virginiae 具有一种活性,可以立体特异性地还原 VM1 的 16-羰基,从而形成抗生素不活性的 16R-二氢 VM1。从 S. virginiae 的粗提物中,经过五个步骤纯化得到相应的 VM1 还原酶,纯度为 5,650 倍,总收率为 23%。其 N-末端氨基酸序列为 MAIKLVIA。纯化的酶在十二烷基硫酸钠-聚丙烯酰胺凝胶电泳中表现出明显的分子量为 73,000,并且在天然分子筛高效液相色谱中表现出分子量为 280,000,表明天然酶的四聚体性质。NADPH 作为还原的辅酶,其 Km 值为 0.13 mM,但是即使在 5 mM 的浓度下,NADH 也不能支持反应,表明该酶具有 NADPH 特异性。在 2 mM NADPH 存在下,VM1 的 Km 值为 1.5 mM。在反向反应中,只有 16R-二氢 VM1 而不是 16S-表异构体作为底物,其反应速率仅相当于正向反应的不到 0.1%,从而确认 VM1 还原酶仅参与 VM1 在体内的失活。