牛蛙變態過程中胰澱粉?之合成及其活性之變化

Abstract

根據前人報告（2）指出，牛蛙 (Rana catesbeiana)蝌蚪的胰臟（ pancreas ) 在變態過程中其大小，形狀結構等各方面都有顯著的變化。胰臟所分泌的酵素之一，胰澱粉?（ pancreatic amylase ) ，是分解碳水化合物的主要酵素。由於蝌蚪在後來的變態階段，由草食性轉變為肉食性，所以研究其澱粉?在變態階段之消長可以獲知更多有關變態之訊息。 本論文將牛蛙蝌蚪在四個主要階段：變態前階段（premetamorphosis）、變態中階段（ prometamorphosis ）、變態高潮（ climax ）及變態後階段 ( postmetamorphosis ) (3)分析其胰澱粉?活性之消長及全部核醣核酸（ total RNA ）中傳訊核醣核酸（ m RNA ）的變化。期盼能由此建立一個變態新參數。 研究結果發現，在自然的變態過程中，蝌蚪胰澱粉?的活性逐漸降低，到變態高潮時幾乎完全消失，然後又漸恢復其活性。而以老鼠的α－澱粉?互補去氧核醣核酸（ c DNA ）當做探針測定其胰澱粉?mRNA 之含量，發現它與酵素活性的消長有大致平行的變化。有趣的是，經T4 水溶液（ 20nM ）浸泡而變態的蝌蚪，則表現不同的結果。又更進一步對不同變態階段的蝌蚪胰臟可溶性蛋白做電泳分析，發現有二蛋白質（分子量約 38kDa 與 45kDa ）在達變態高潮時即消失不見。其中－蛋白質 ( 38kDa ）經部分胺基酸定序分析，其 N 一端18個序列與現有蛋白質資料庫比對未發現有類似的序列。它可能是與蝌蚪變態有關的－個蛋白質。

The study of amphibian metamorphosis has a long history. It has come to be realized that the thyroid hormone, adrenocorticoid hormone and prolactin are involved in the process (1). The thyroid hormone has been investigated as the major hormone that stimulates the metamorphosis. During the period of metamorphosis, there are different gene expressions in the tissues, such as: limbs, liver, skin, and nervous system. According to the earlier report (2), the size, shape, and structure of Rana catesbeiana tadpole pancreas have significantly changed during metamporphosis. Pancreatic amylases are the major enzymes in the digestion and absorption of carbohydrate and since the tadpole changes from herbivore into carnivore during the metamorphosis, the amylase activity and expression level may be regulated during metamorphosis. The amylase activity and its mRNA of bullfrog tadpole at four stages: premeatmorphosis, prometamorphosis, climax, and postmetamorphosis (3) were determined and compared. It was found that the amylase activity gradually decreased during metamorphosis and almost disappeared at the climax stage of metamorphosis. By using rat α-amylase cDNA as probe, the level of pancreatic α-amylase mRNA was found to change with the same pattern as that of amylase activity. It is interesting that different result was obtained if the tadpole was treated with T4 solution (20nM) to induce metamorphosis. When the soluble protein extract from tadpole pancreas was analyzed, two proteins (about 38kDa and 45kDa) were found to disapear at the climax stage implying that this protein may be involved in metamorphosis. The protein (38kDa) was subjected to N-terminal sequence analysis and no homologous sequence was found when the protein data bank was searched.