ABSTRACT
Pseudomonas
sp. strain KIE171 was able to grow with isopropylamine or
l
-alaninol [
S
-(+)-2-amino-1-propanol] as the sole carbon source, but not with
d
-alaninol. To investigate the hypothesis that
l
-alaninol is an intermediate in the degradation of isopropylamine, two mini-Tn
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mutants unable to utilize both isopropylamine and
l
-alaninol were isolated. Whereas mutant KIE171-BI transformed isopropylamine to
l
-alaninol, mutant KIE171-BII failed to do so. The two genes containing a transposon insertion were cloned, and the DNA regions flanking the insertions were sequenced. Two clusters, one comprising eight
ipu
(isopropylamine utilization) genes (
ipuABCDEFGH
) and the other encompassing two genes (
ipuI
and
orf259
), were identified. Comparisons of sequences of the deduced Ipu proteins and those in the database suggested that isopropylamine is transported into the cytoplasm by a putative permease, IpuG. The next step, the formation of γ-glutamyl-isopropylamide from isopropylamine, ATP, and
l
-glutamate, was shown to be catalyzed by IpuC, a γ-glutamylamide synthetase. γ-Glutamyl-isopropylamide is then subjected to stereospecific monooxygenation by the hypothetical four-component system IpuABDE, thereby yielding γ-glutamyl-
l
-alaninol [γ(
l
-glutamyl)-
l
-hydroxy-isopropylamide]. Enzymatic hydrolysis by a hydrolase, IpuF, was shown to finally liberate
l
-alaninol and to regenerate
l
-glutamate. No gene(s) encoding an enzyme for the next step in the degradation of isopropylamine was found in the
ipu
clusters. Presumably,
l
-alaninol is oxidized by an alcohol dehydrogenase to yield
l
-2-aminopropionaldehyde or it is deaminated by an ammonia lyase to propionaldehyde. Genetic evidence indicated that the aldehyde formed is then further oxidized by the hypothetical aldehyde dehydrogenases IpuI and IpuH to either
l
-alanine or propionic acid, compounds which can be processed by reactions of the intermediary metabolism.
摘要
假单胞菌
菌株 KIE171 能够在异丙胺或
l
-丙氨醇[
S
-(+)-2-氨基-1-丙醇] 作为唯一碳源,但不能以
d
-丙醇作为唯一碳源。为了研究
l
-丙氨醇是异丙基胺降解过程中的一个中间体这一假设进行了研究。
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突变体不能同时利用异丙基胺和
l
-丙氨醇的中间体。而突变体 KIE171-BI 将异丙基胺转化为 l -丙氨醇。
l
-丙氨醇,而突变体 KIE171-BII 却不能做到这一点。克隆了含有转座子插入的两个基因,并对插入侧翼的 DNA 区域进行了测序。两个基因簇,一个由八个
ipu
(异丙基胺利用)基因 (
ipuABCDEFGH
),另一个包括两个基因 (
ipuI
和
orf259
)。对推导出的 Ipu 蛋白的序列和数据库中的序列进行比较后发现,异丙基胺是通过一种假定的渗透酶 IpuG 转运到细胞质中的。下一步是由异丙基胺、ATP 和γ-谷氨酰-异丙基酰胺形成γ-谷氨酰-异丙基酰胺。
l
-γ-谷氨酰-异丙基酰胺然后由假定的四组分系统 IpuABDE 进行立体特异性单氧合反应,从而产生γ-谷氨酰-异丙基酰胺。
l
-丙氨醇[γ(
l
-谷氨酰)-
l
-羟基异丙基酰胺]。研究表明,水解酶 IpuF 的酶促水解最终会释放出
l
-丙氨醇,并再生出
l
-谷氨酸。在 IpuF 中没有发现编码异丙基胺下一步降解酶的基因。
ipu
簇中没有发现编码异丙基胺下一步降解酶的基因。推测
l
-丙氨醇被醇脱氢酶氧化,生成
l
-2-氨基丙醛,或者被氨裂解酶脱氨成丙醛。遗传学证据表明,形成的醛随后会被假定的醛脱氢酶 IpuI 和 IpuH 进一步氧化,生成 l -2 -氨基丙醛或 l -2 -氨基丙醛。
l
-丙氨酸或丙酸,这些化合物可通过中间代谢反应进行处理。