Several growth characteristics of
Escherichia coli
K-12 suggest that growth on
l
-fucose results in the synthesis of all the enzymes necessary for growth on
d
-arabinose. Conversely, when a mutant of
E. coli
is grown on
d
-arabinose, all of the enzymes necessary for immediate growth on
l
-fucose are present. Three enzymes of the
l
-fucose pathway in
E. coli
,
l
-fucose isomerase,
l
-fuculokinase, and
l
-fuculose-l-phospháte aldolase possess activity on
d
-arabinose,
d
-ribulose, and
d
-ribulose-l-phosphate, respectively. The products of the aldolase, with
d
-ribulose-l-phosphate as substrate, are dihydroxyacetone phosphate and glycolaldehyde.
l
-Fucose, but not
d
-arabinose, is capable of inducing these activities in wild-type
E. coli
. In mutants capable of utilizing
d
-arabinose as sole source of carbon and energy, these activities are induced in the presence of
d
-arabinose and in the presence of
l
-fucose. Mutants unable to utilize
l
-fucose, selected from strains capable of growth on
d
-arabinose, are found to have lost the ability to grow on
d
-arabinose. Enzymatic analysis of cell-free extracts, prepared from cultures of these mutants, reveals that a deficiency in any of the
l
-fucose pathway enzymes results in the loss of ability to utilize
d
-arabinose. Thus, the pathway of
d
-arabinose catabolism in
E. coli
K-12 is believed to be:
d
-arabinose ⇌
d
-ribulose →
d
-ribulose-l-phosphate ⇌ dihydroxyacetone phosphate plus glycolaldehyde. Evidence is presented which suggests that the glycolaldehyde is further oxidized to glycolate.
大肠杆菌K-12的几个生长特征表明,在L-岩藻糖上生长会导致合成生长所需的D-阿拉伯糖酶。相反,当大肠杆菌的突变体在D-阿拉伯糖上生长时,即可立即合成生长所需的L-岩藻糖酶。大肠杆菌中L-岩藻糖途径的三种酶,即L-岩藻糖异构酶、L-岩藻糖激酶和L-岩藻糖醛酸酯酶,分别对D-阿拉伯糖、D-核糖醇和D-核糖醇-1-磷酸具有活性。以D-核糖醛酸为底物的醛酸酯的产物是二羟基乙酮磷酸和甘醛。L-岩藻糖而不是D-阿拉伯糖能够在野生型大肠杆菌中诱导这些活性。在能够利用D-阿拉伯糖作为碳和能源的突变体中,在D-阿拉伯糖和L-岩藻糖存在的情况下,这些活性被诱导。从能够在D-阿拉伯糖上生长的菌株中选择无法利用L-岩藻糖的突变体,发现它们已经失去了在D-阿拉伯糖上生长的能力。从这些突变体培养物中制备的细胞游离提取物的酶分析表明,任何L-岩藻糖途径酶的缺乏都会导致无法利用D-阿拉伯糖。因此,D-阿拉伯糖在大肠杆菌K-12中的分解途径被认为是:D-阿拉伯糖 ⇌ D-核糖醛糖 → D-核糖醛糖-1-磷酸 ⇌ 二羟基乙酮磷酸和甘醛。提供了证据表明,甘醛进一步被氧化为甘酸。