Jackson Frances M, Michaelson Louise, Fraser Thomas C M, Stobart A Keith, Griffiths Gareth
School of Biological Sciences, University of BristolWoodland Road, Bristol BS8 1UGUK.
Department of Plant Genetics and Biotechnology, Horticulture Research InternationalWellesbourne, Warwickshire CV35 9EFUK.
Microbiology (Reading). 1998 Sep;144 ( Pt 9):2639-2645. doi: 10.1099/00221287-144-9-2639.
Lipid metabolism was studied in 2-d-old liquid cultures of Mucor circinelloides grown at 25 degrees C. Under these conditions, oil accumulated to 0.5 g l-1 with a gamma-linolenic acid content (gamma 18:3) of 60 mg l-1. The major labelled lipids in cultures incubated with [14C]acetate were triacylglycerol (TAG), phosphatidylcholine (PC) and phosphatidylethanolamine (PE). The proportion of label declined in the phospholipids and increased in TAG with time. [14C]18:1 and [14C]18:2 rapidly appeared in PC and PE and later accumulated in [14C]gamma 18:3. TAG-synthesizing capacity was greatest in the microsomal membrane fraction, which accumulated high levels of phosphatidic acid in the presence of glycerol 3-phosphate and acyl-CoA substrates at pH 7.0. Further metabolism of phosphatidic acid to diacylglycerol and TAG was achieved by increasing the pH to 8.0. Lysophosphatidic acid: acyl-CoA acyltransferase (LPAAT) activity was particularly high and may have accounted for the rapid accumulation of phosphatidic acid in the membranes. The glycerol-3-phosphate: acyl-CoA acyltransferase (GPAAT) and LPAAT were non-specific for a range of saturated and unsaturated species of acyl-CoA although the GPAAT showed a marked selectivity for palmitoyl-CoA and the LPAAT for oleoyl- and linoleoyl-CoA. gamma-Linolenic acid was detected at all three positions of sn-TAG and was particularly enriched at the sn-3 position. The preparation of active in vitro systems (microsomal membranes) capable of the complete biosynthetic pathway for TAG assembly may be valuable in understanding the assembly of oils in future transgenic applications.
在25摄氏度下培养的2日龄卷枝毛霉液体培养物中研究了脂质代谢。在这些条件下，油脂积累至0.5 g l-1，γ-亚麻酸含量（γ18:3）为60 mg l-1。用[14C]乙酸盐培养的培养物中主要的标记脂质是三酰甘油（TAG）、磷脂酰胆碱（PC）和磷脂酰乙醇胺（PE）。随着时间的推移，磷脂中的标记比例下降，而TAG中的标记比例增加。[14C]18:1和[14C]18:2迅速出现在PC和PE中，随后在[14C]γ18:3中积累。TAG合成能力在微粒体膜部分最强，在pH 7.0时，在甘油3-磷酸和酰基辅酶A底物存在的情况下，该部分积累了高水平的磷脂酸。通过将pH提高到8.0，磷脂酸进一步代谢为二酰甘油和TAG。溶血磷脂酸：酰基辅酶A酰基转移酶（LPAAT）活性特别高，可能是膜中磷脂酸快速积累的原因。甘油-3-磷酸：酰基辅酶A酰基转移酶（GPAAT）和LPAAT对一系列饱和和不饱和的酰基辅酶A种类不具有特异性，尽管GPAAT对棕榈酰辅酶A表现出明显的选择性，而LPAAT对油酰辅酶A和亚油酰辅酶A表现出选择性。在sn-TAG的所有三个位置都检测到了γ-亚麻酸，并且在sn-3位置特别富集。能够进行TAG组装完整生物合成途径的活性体外系统（微粒体膜）的制备，对于理解未来转基因应用中油脂的组装可能具有重要价值。
