Department of Biology, University of California, San Diego, La Jolla, California 92093.
Plant Physiol. 1983 Jan;71(1):82-7. doi: 10.1104/pp.71.1.82.
Cotyledons of maturing Phaseolus vulgaris seeds contain three isozymes of alpha-mannosidase which can be separated by isoelectrofocusing. They have isoelectric points of 5.3, 5.8, and 6.5 to 7.5 and were named I, II, and III in order of ascending pI. All three had an acid pH optimum (4.5) and required Zn(2+) for maximal activity. Isozymes I and II were present in the protein bodies. Together they accounted for 85% of the total activity. Isozyme III was essentially absent from isolated protoplasts but could be extracted from isolated cell walls. All three isozymes were also found to be associated with the endoplasmic reticulum, and the proportion of the total activity in this fraction decreased from 20% in immature cotyledons to 6% in mature cotyledons. The results are interpreted as evidence that newly synthesized alpha-mannosidase is sequestered in the lumen of the ER prior to its transport to the protein bodies or the cell wall.
成熟菜豆种子的子叶中含有三种α-甘露糖苷酶同工酶，可通过等电聚焦分离。它们的等电点分别为 5.3、5.8 和 6.5 至 7.5，并按 pI 值递增的顺序分别命名为 I、II 和 III。这三种同工酶的最适 pH 值均为酸性（4.5），且需要 Zn(2+) 才能达到最大活性。同工酶 I 和 II 存在于蛋白体中。它们共同占总活性的 85%。同工酶 III 基本上不存在于分离的原生质体中，但可以从分离的细胞壁中提取出来。还发现这三种同工酶都与内质网有关，该部分的总活性比例从未成熟子叶的 20%下降到成熟子叶的 6%。结果表明，新合成的α-甘露糖苷酶在运输到蛋白体或细胞壁之前，先被隔离在内质网的腔室中。
