Rosenfield C L, Loewus F A
Department of Biological Sciences, State University of New York, Buffalo, New York 14214.
Plant Physiol. 1978 Jan;61(1):96-100. doi: 10.1104/pp.61.1.96.
myo-Inositol-linked glucogenesis in germinated lily (Lilium longiflorum Thunb., cv. Ace) pollen was investigated by studying the effects of added l-arabinose or d-xylose on metabolism of myo-[2-(3)H]inositol and by determining the distribution of radioisotope in pentosyl and hexosyl residues of polysaccharides from pollen labeled with myo-[2-(14)C]inositol, myo-[2-(3)H]inositol, l-[5-(14)C]arabinose, and d-[5R,5S-(3)H]xylose.myo-[2-(14)C]Inositol and l-[5-(14)C]arabinose produced labeled glucose with similar patterns of distribution of (14)C, 35% in C1, and 55% in C6. Arabinosyl units were labeled exclusively in C5. Incorporation of (3)H into arabinosyl and xylosyl units in pollen labeled with myo-[2-(3)H]inositol was repressed when unlabeled l-arabinose was included in the germination medium and a related (3)H exchange with water was stimulated. Results are consistent with a process of glucogenesis in which the myo-inositol oxidation pathway furnishes UDP-d-xylose as a key intermediate for conversion to hexose via free d-xylose and the pentose phosphate pathway.Additional evidence for this process was obtained from pollen labeled with d-[5R,5S-(3)H]xylose or myo-[2-(3)H]inositol which produces d-[5R-(3)H]xylose. Glucosyl units from polysaccharides in the former had 11% of the (3)H in C1 and 78% in C6 while glucosyl units in the latter had only 4% in C1 and 78% in C6. Stereochemical considerations involving selective exchange with water of prochiral-R (3)H in C1 of fructose-6-P during conversion to glucose provide explanation for observed differences in the metabolism of these 5-labeled xyloses.Incorporation of (3)H from myo-[2-(3)H]inositol into arabinosyl and xylosyl units of pollen polysaccharides was unaffected by the presence of unlabeled d-xylose in the medium. Exchange of (3)H with water was greatly affected, decreasing from a value of 21% exchange in the absence of unlabeled d-xylose to 5% in the presence of 6.7 mmd-xylose.d-Xylose was rapidly utilized for glucogenesis by germinated pollen tubes. This observation supports the view that free d-xylose is an important intermediate following breakdown of UDP-d-xylose during myo-inositol-linked glucogenesis.
通过研究添加L-阿拉伯糖或D-木糖对肌醇-[2-(³H)]肌醇代谢的影响，并测定用肌醇-[2-(¹⁴C)]肌醇、肌醇-[2-(³H)]肌醇、L-[5-(¹⁴C)]阿拉伯糖和D-[5R,5S-(³H)]木糖标记的花粉中多糖的戊糖基和己糖基残基中放射性同位素的分布，对发芽百合（麝香百合，品种Ace）花粉中肌醇连接的糖异生作用进行了研究。肌醇-[2-(¹⁴C)]肌醇和L-[5-(¹⁴C)]阿拉伯糖产生标记葡萄糖，其¹⁴C分布模式相似，C1中为35%，C6中为55%。阿拉伯糖基单元仅在C5处被标记。当在发芽培养基中加入未标记的L-阿拉伯糖时，用肌醇-[2-(³H)]肌醇标记的花粉中³H掺入阿拉伯糖基和木糖基单元的过程受到抑制，并且刺激了与水的相关³H交换。结果与糖异生过程一致，在该过程中，肌醇氧化途径提供UDP-D-木糖作为通过游离D-木糖和戊糖磷酸途径转化为己糖的关键中间体。从用D-[5R,5S-(³H)]木糖或肌醇-[2-(³H)]肌醇标记的花粉中获得了该过程的额外证据，这两种标记产生D-[5R-(³H)]木糖。前者多糖中的葡萄糖基单元在C1中有11%的³H，在C6中有78%，而后者中的葡萄糖基单元在C1中只有4%，在C6中有78%。在转化为葡萄糖过程中，涉及果糖-6-P的C1中前手性-R³H与水的选择性交换的立体化学考虑为观察到的这些5-标记木糖代谢差异提供了解释。培养基中未标记的D-木糖的存在不影响肌醇-[2-(³H)]肌醇中³H掺入花粉多糖的阿拉伯糖基和木糖基单元。³H与水的交换受到很大影响，从未标记D-木糖时的21%交换值降至存在6.7 mmol/L D-木糖时的5%。D-木糖被发芽的花粉管迅速用于糖异生。这一观察结果支持了这样一种观点，即游离D-木糖是肌醇连接的糖异生过程中UDP-D-木糖分解后的重要中间体。
