Denyer K, Dunlap F, Thorbjørnsen T, Keeling P, Smith A M
John Innes Centre, Norwich Research Park, Colney, Norfolk, United Kingdom.
Plant Physiol. 1996 Oct;112(2):779-85. doi: 10.1104/pp.112.2.779.
Preparations enriched in plastids were used to investigate the location of ADP-glucose pyrophosphorylase (AGPase) in the developing endosperm of maize (Zea mays L.). These preparations contained more than 25% of the total activity of the plastid marker enzymes alkaline pyrophosphatase and soluble starch synthase, less than 2% of the cytosolic marker enzymes alcohol dehydrogenase and pyrophosphate, fructose 6-phosphate 1-phosphotransferase, and approximately 3% of the AGPase activity. Comparison with the marker enzyme distribution suggests that more than 95% of the activity of AGPase in maize endosperm is extra-plastidial. Two proteins were recognized by antibodies to the small subunit of AGPase from maize endosperm Brittle-2 (Bt2). The larger of the two proteins was the major small subunit in homogenates of maize endosperm, and the smaller, less abundant of the two proteins was enriched in preparations containing plastids. These results suggest that there are distinct plastidial and cytosolic forms of AGPase, which are composed of different subunits. Consistent with this was the finding that the bt2 mutation specifically eliminated the extraplastidial AGPase activity and the larger of the two proteins recognized by the antibody to the Bt2 subunit.
富含质体的制剂被用于研究玉米（Zea mays L.）发育中的胚乳中ADP - 葡萄糖焦磷酸化酶（AGPase）的定位。这些制剂含有超过25%的质体标记酶碱性焦磷酸酶和可溶性淀粉合酶的总活性，少于2%的胞质标记酶乙醇脱氢酶和焦磷酸、果糖6 - 磷酸1 - 磷酸转移酶，以及约3%的AGPase活性。与标记酶分布的比较表明，玉米胚乳中超过95%的AGPase活性存在于质体外。玉米胚乳脆性2（Bt2）的AGPase小亚基抗体识别出两种蛋白质。这两种蛋白质中较大的是玉米胚乳匀浆中的主要小亚基，而较小且含量较少的那种蛋白质在含有质体的制剂中富集。这些结果表明存在由不同亚基组成的不同的质体形式和胞质形式的AGPase。与此一致的是，bt2突变特异性地消除了质体外的AGPase活性以及被Bt2亚基抗体识别的两种蛋白质中较大的那种。
