| The main aim of the present work was to lay foundations for further understanding the effect of hydrogen peroxide(H202) on Rubisco degradation with the study of relationship between endopeptidases and H202 during wheat leaves aging and characteristics of endopeptidases extracted from chloropLast stroma of wheat seedlings. At first, a sensitive and generally applicable substrate-containing gradient gel electrophoresis method for detection of endopeptidases in biological preparations was developed. It can be used to study the type, molecular weight and activity .of endopeptidases. Combined with the isolation of organelles, the method can also be used to study the location cf endopeptidases. Compared with other electrophoresis methods, it has higher reso~ution power and wider scope of application. Then, the relationship between H202 and endopeptidases in wheat leaves was studied during natural and artificial aging. Rapid accumulation of endogenous H202 and marked increase of endopeptidases activity were observed during the later phase of aging. A new endopeptidases with higher activity was detected by electrophoresis on polyacrylamide gradient gels containing denatured hearnoglobin. With increase of exogenous H202, the activity of endopeptidases increased at first and then decreased. Finally, to know more about the degradation of Rubisco in vivo, the endopeptidases(EPs) from chloroplasts of wheat seedlings were studied. Two endopeptidases were identified by electrophoresis on polyacrylamide gradient gels containing denatured heamoglobin in the chloroplast stroma. Their molecular 2 weights were 66KD and S4KD, respectively. Their activity was completely inhibited by 1 mmol/L phenylmethylsulphonyl fluoride (PMSF). Actidione prevented the synthesis of the two endopeptidases, but chlorarnphenicol had no apparent effect on their synthesis. The optium pH of endopeptidases extracted from chloroplasts was 7.5, the optium temperature was 42C. Its activity was enhanced by lmmolIL ATP or DTT.
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