The metabolism of L-proline by jack pine seedlings

Abstract

The metabolism of L-proline was studied in 6-day-old jack pine seedlings, freshly excised from the nutritive female gametophyte. During the following 24 h, a sharp drop in free amino acids and protein was observed. Although levels of free proline were low, uniformly labeled 14C-L-proline and proline-3, 4-3H served as precursors for the dicarboxylic amino acids and their corresponding amides, glutamine and asparagine, which usually accumulate during germination. The origin of asparagine while unresolved did not involve β-cyanoalanine. Other products of proline metabolism included Δ1-pyrroline-5-carboxylic acid, glutamic acid, and γ-aminobutyric acid. With 14C-proline, radioactivity in alanine and serine resulted presumably from refixation of 14CO2 that was released by the decarboxylation of glutamic acid and other organic acids. The remaining products, e.g. pyrrolidone carboxylic acid, succinamic acid, and succinimide, were more closely related to the fate of glutamine than to proline.Radioactivity in proline and derived amino acids was recovered from soluble proteins separated on polyacrylamide gels. Five fractions revealed a similar diurnal turnover of specific activity. Three of these contained peroxidase isoenzyme activity. The recovery of tritium from peroxidase isoenzymes was related through the metabolism of proline to the intake and metabolism of water as well as to the appearance of enzyme activity in vascular tissues and emerging root and shoot apices.