玉米细胞质分子伴侣Hsp70 的ATPase 活性

ATPase Activity of Cytosolic Chaperone Hsp70 from Maize Endosperm Cell

玉米胚乳细胞中纯化的细胞质Ｈｓｐ７０蛋白有低水平的ＡＴＰａｓｅ 活性，它在５０ ℃、ｐＨ５ ．８ 、２０ ｍｍｏｌ／Ｌ的ＫＣｌ 条件下活性最高，Ｃａ２＋和Ｍｇ２＋ 抑制其活性。大肠杆菌ＤｎａＪ蛋白能将玉米细胞质Ｈｓｐ７０ 的ＡＴＰａｓｅ 活性提高６倍，而ＧｒｐＥ 蛋白对其影响很小。８ 种不同的人工合成多肽均能刺激该蛋白的ＡＴＰａｓｅ 活性，增加幅度从２ ．５ 倍到１０ 倍不等。亲水性不同的氨基酸对Ｈｓｐ７０ 的ＡＴＰａｓｅ 活性影响不同。玉米细胞质Ｈｓｐ７０ 是一个三磷酸核苷酸酶，除ＡＴＰ 外，它还能催化ＵＴＰ、ＧＴＰ。

The cytosolic chaperone Hsp70 protein from maize endosperm cell was purified. The Hsp70 have a low level ATPase activity at normal temperature. In vitro the ATPase activity of the Hsp70 was maximal at 50℃, pH 5.8, and a KCl concentration of 20 mmol/L(Figs.2～4). It's activity was decreased with increasing concentration of magnesium or calcium from 0 to 20 mmol/L(Fig.5). The co chaperone protein from E. coli , DnaJ protein, increased the ATPase activity of maize Hsp70 about 6 fold, while GrpE, also a co chaperone protein from E.coli , had no effect(Figs.6,7). The ATPase activity of maize Hsp70 was stimulated by incubation with short synthetic peptides studied. At a final concentration of 400 μmol/L, peptide stimulation of ATPase activity was between 2.5～10 fold(Table 1).Isoleucine, an amino acid with high hydrophobicity, increased the ATPase activity of maize Hsp70 2.5 fold,while asparagine,an amino acid with high hydrophilia, had no effect on ATPase activity of Hsp70(Fig.8). Hsp70 proteins are actually nucleoside triphosphatases. Besides ATP, UTP,GTP, CTP and ITP were also hydrolized by cytosolic Hsp70 of maize cells(Fig.9).