Regulation Of Carbohydrate Metabolic Enzymes By Protein Reversible Phosphorylation In Apple Fruit

Ptotein phosphorylation plays an important role in signal transduction and regulation. In the past decade, numerous research found out there were different kinds of protein kinases and protein phosphatases in plant cell. One of their main function is regulating activity of metabolic enzymes. In this paper, by using ATP to treat crude exact of apple fruit and observing the effect on several metabolic enzymes, we identified four of them might be regulated by protein phosphorylation: sucrose phosphate synthase (SPS), sucrose synthase (SS) with two reaction, and amylase. By adding inhibitors of some protein kinases and protein phosphatases, our results showed that there may exist covalent modification in apple fruit. Meanwhile, their types or characteristics had been inferred.ABA is such an important plant hormone which controls developing and ripening of almost all fruits. In addition, carbohydrate unloading is also regulated by ABA. Therefore, it is of important to make clear if ABA has effect on metabolic enzymes. By inhubating fruit slices with ABA for 4 hours, we assayed the activity of several metabolic enzymes. From the data we'd gotten, three of them were activated remarkably: acid invertase, sorbitol oxidase and sucrose synthase ( cleavage reaction). While SPS and SS (formation reaction) just be activated slightly, and no change was found in amylase and sorbital dehydrogenase. These results indicated that, as a signal molecular, ABA probably regulated many genes expression or induced some reactions during inhubation and, then, influenced the activity of the enzymes above.In order to testify if the signal transduction induced by ABA contained protein reversible phosphorylation modification, we use alkaline phosphatase to treat the enzymes exacted from fruit slices (inhubated with 20umol/L ABA). Acid invertase and SS(cleavage reaction) were greatly activated further. It is interesting that we got the same results after adding inhibitors of protein kinases. Hence, dephosphorylation helped to enhance the activity of two enzymes. Because of the random results from the treatment of inhibitors of protein phosphatases, we inferred that there were complex regulation mechanism in apple fruit developing.As a mechanism of switch, protein phosphorylation has universality in plant. However, to date, there is no report about metabolic enzymes regulation by such modification in apple fruit. In this paper, we find the relation between the signal transduction induced by ABA and the reversible protein phosphorylation and inferred possible method of covalent regulation of carbohydrate metabolic enzymes in apple fruit as well.