Figure 1.

Schematic diagram showing several nonenzymatic mechanisms that could affect protein structure and function in aging potato tubers. Protein modifications that may accompany aging include oxidation (increased carbonyl groups), glycation (reaction of amino acids with reducing sugars leading to protein cross-linking), and deamidation/isomerization/racemization of asparaginyl and aspartyl residues. Although these molecular modifications can target proteins for proteolysis, deamidation-mediated increases in isoaspartyl residues creates substrates for PCMT-II, which can restore function of the affected proteins. Effects of tuber age on such molecular modifications are presented in Figures 9 and 10 and Table III.