萌发绿豆子叶衰老期间蛋白质代谢的变化

萌发绿豆子叶自然衰老过程中可溶性蛋白质含量一直下降;从衰老开始到衰老前期,总游离氨基酸含量明显上升;但游离氨基酸各组分在子叶衰老期间的变化趋势并不相同。~3H-亮氨酸掺入蛋白质试验和多聚核糖体的相对量及其与总核糖体的比值(P/T)测定都证明在子叶衰老前期有蛋白质的新合成。子叶衰老期间。氨肽酶活性明显降低;而以酪蛋白为底物的蛋白水解酶活性却急剧上升,承担着催化蛋白质降解的主要功能。

Changes in Protein Metabolism During Senescence of Mung Bean Cotyledons

Changes in the contents of soluble proteins and free amino acids, the synthesis of protein, and proteolytic activity during senescence of mung bean cotyledons were investigated in this study. The results are as follows:From day 1 to day 7 after germination, the contents of soluble proteins markedly decreased while the contents of total free amino acids increased from day 1 to 5 and then declined (Fig. 1). It is worth noting that the patterns of change in individual amino acids were not the same. The complexity of different free amino acids implied that the components played different roles in regulating the senescence of mung bean cotyledons.The incorporation of ~3H-leucine into protein showed that the rate of protein synthesis increased after the onset of senescence and reached the top by the 4th day (Fig. 2). Analysis of ribosomal population and calculation of the ratio of polysomes to total ribosomes (P/T) revealed a similar trend to that of ~3H-leucine incorporation (Fig. 3 , Table 2 ). All these results suggested that the synthesis of protein was active during the early staage of senescence of mung bean cotyledons.The activity of leucine aminopeptidase decreased from day 1 to day 7.However, the caseolytic activity of mung bean cotyledons increased rapidly during the early stage of senescence and decreased sharply after day 5 (Fig. 5). Thus, it may be concluded that the loss of soluble proteins during early senescence can be ascribed to accelerated hydrolysis by endopeptidases and the slowdown of protein synthesis was mainly responsible for the decline of soluble proteins during late senescence.