Juang R H, McCue K F, Ow D W
Plant Gene Expression Center, U.S. Department of Agriculture, Albany, California.
Arch Biochem Biophys. 1993 Aug 1;304(2):392-401. doi: 10.1006/abbi.1993.1367.
In plants and in certain fungi, exposure to heavy metals induces the synthesis of metal-binding peptides commonly known as phytochelatins. With cadmium, phytochelatins can sequester the metal into a sulfide-containing complex. From genetic analysis of fission yeast mutants, we previously reported that two genes in purine biosynthesis, encoding adenylosuccinate synthetase and succinoaminoimidazole carboxamide ribonucleotide (SAICAR) synthetase, are required for the biogenesis of the phytochelatin-cadmium-sulfide complex in vivo. We suggested that a sulfur analog of aspartate, cysteine sulfinate, might be utilized by these enzymes and that the cysteine sulfinate-derived products would then become intermediates or carriers in a sulfur transfer pathway leading to the sulfide found within the metal chelate. In this paper, we report that partially purified adenylosuccinate synthetase and SAICAR synthetase are capable of utilizing cysteine sulfinate in vitro to form sulfur analog products. Adenylosuccinate lyase, however, fails to catalyze further conversion of these sulfur derivatives. These observations support the genetic data implicating a link among purine biosynthetic enzymes, sulfur metabolism, and cadmium tolerance.
在植物和某些真菌中，暴露于重金属会诱导通常被称为植物螯合肽的金属结合肽的合成。对于镉，植物螯合肽可以将金属螯合到含硫化物的复合物中。通过对裂殖酵母突变体的遗传分析，我们先前报道嘌呤生物合成中的两个基因，分别编码腺苷酸琥珀酸合成酶和琥珀酰氨基咪唑甲酰胺核糖核苷酸（SAICAR）合成酶，是体内植物螯合肽 - 镉 - 硫化物复合物生物合成所必需的。我们推测天冬氨酸的硫类似物半胱亚磺酸可能被这些酶利用，并且半胱亚磺酸衍生的产物随后会成为硫转移途径中的中间体或载体，该途径会导致金属螯合物中存在的硫化物。在本文中，我们报道部分纯化的腺苷酸琥珀酸合成酶和SAICAR合成酶能够在体外利用半胱亚磺酸形成硫类似物产物。然而，腺苷酸琥珀酸裂解酶无法催化这些硫衍生物的进一步转化。这些观察结果支持了遗传数据，表明嘌呤生物合成酶、硫代谢和镉耐受性之间存在联系。
