Salerno G L, Echeverria E, Pontis H G
Centro de Investigaciones Biológicas, Fundación para Investigaciones Biológicas Aplicadas, Mar del Plata, Argentina.
Cell Mol Biol (Noisy-le-grand). 1996 Jul;42(5):665-72.
The possible presence of a sucrose-phosphate synthase (SPS) activating/stabilizing factor (SAF) presumably lost during SPS purification was investigated. Rice leaf protein extracts were chromatographed in a DEAE-Sephacel column. SPS activity of previously purified rice enzyme was enhanced to different extent by aliquots of fractions from such column. The activating capacity could not be replaced by albumin, but was nullified by EDTA. When the fractions were boiled or treated with TCA, the activating capacity disappeared suggesting its proteinaceous nature. The presence of 10 microM okadaic acid had no effect on the stimulatory action of SAF on SPS denying the possibility to SAF to be a SPS-phosphatase. Although it overlaps somehow with sucrose synthase (SS) in DEAE-Sephacel fractions, the activating protein factor and SS eluted separately during Sephadex G-200 chromatography. The activating ability was saturable at a fixed SPS concentration and was able to enhance SPS activity from other plant sources. Simultaneous studies on the activities of SPS and sucrose-phosphate phosphatase (SPP), closely linked to SPS, allowed us to suggest that SAF could be SPP. The presence of SAF/SPP did not alter the affinity of SPS for its substrates but helped to reverse the Pi inhibition at low Fru-6-P concentrations. We conclude that SPS may possibly interact with SPP, contributing to a more effective sucrose synthesis.
对蔗糖磷酸合酶（SPS）激活/稳定因子（SAF）可能在SPS纯化过程中丢失的情况进行了研究。水稻叶片蛋白提取物在DEAE-琼脂糖凝胶柱上进行色谱分析。来自该柱的各部分等分试样能不同程度地增强先前纯化的水稻酶的SPS活性。白蛋白不能替代这种激活能力，但EDTA可使其丧失。当这些部分煮沸或用三氯乙酸处理时，激活能力消失，表明其具有蛋白质性质。10微摩尔冈田酸的存在对SAF对SPS的刺激作用没有影响，排除了SAF是一种SPS磷酸酶的可能性。尽管在DEAE-琼脂糖凝胶部分它与蔗糖合酶（SS）有一定程度的重叠，但在葡聚糖G-200色谱分析过程中，激活蛋白因子和SS是分别洗脱的。在固定的SPS浓度下，激活能力是可饱和的，并且能够增强其他植物来源的SPS活性。对与SPS紧密相关的SPS和蔗糖磷酸磷酸酶（SPP）活性的同时研究使我们推测SAF可能是SPP。SAF/SPP的存在并未改变SPS对其底物的亲和力，但有助于在低果糖-6-磷酸浓度下逆转磷酸根离子的抑制作用。我们得出结论，SPS可能与SPP相互作用，有助于更有效地合成蔗糖。
