Ascorbate oxidase, protein disulfide isomerase, ascorbic acid, dehydroascorbic acid and protein levels in developing wheat kernels and their relationship to protein disulfide bond formation

Developing wheat kernels of three New Zealand wheat cultivars; at one to nine weeks postanthesis (WPA) were analyzed for kernel weight, salt-soluble protein, salt-insoluble protein, ascorbate oxidase (AOX), protein disulfide isomerase (PDI), ascorbic acid (AA), and dehydroascorbic acid (DHA). Kernel weight and salt-soluble protein increased from one to five or six WPA then declined. The amount of salt-insoluble protein per kernel rapidly increased from two to five or six WPA, then remained constant. AOX activity increased from one to two or three WPA then declined to almost zero at seven WPA. PDI activity increased from one to three WPA, stayed constant to six WPA, then declined about 25%. DHA increased from one to two or three WPA then declined to zero at seven WPA. AA increased from one to three or five WPA then declined to zero at seven WPA. When DHA, at similar concentrations (approximate to1 mM) to that found in one to six WPA kernels, was mixed with reduced-gluten proteins, it was reduced to AA. The results are interpreted as a scheme showing that, during the formation of protein-disulfide bonds, electrons are transferred from nascent protein thiols, ultimately to oxygen, through a series of electron carriers including PDI, AA-DHA, and AOX.