Hydrolysis of Ribulose-1,5-bisphosphate Carboxylase by Endoproteinases from Senescing Barley Leaves

Abstract
The flux of radioactivity from 3,4-[14C]methionine into S-adenosyl-l-methionine (SAM), 1-aminocyclopropane-1-carboxylic acid (ACC), spermine, and spermidine while inhibiting conversion of ACC to ethylene by 100 millimolar phosphate and 2 millimolar Co2+ was studied in aged peel discs of orange (Citrus sinensis L. Osbeck) fruit. Inhibition up to 80% of ethylene production by phosphate and cobalt was accompanied by a 3.3 times increase of label in ACC while the radioactivity in SAM was only slightly reduced. Aminoethoxyvinylglycine (AVG) increased the label in SAM by 61% and reduced it in ACC by 47%. Different combinations of standard solution, in which putrescine or spermidine were administered alone or with AVG, demonstrated clearly that inhibition of ethylene biosynthesis—at the conversion of SAM to ACC—by AVG, exogenous putrescine or exogenous spermidine, stimulated the incorporation of 3,4-[14C]methionine into spermidine.