In vitro synthesis of spermidine in the higher plant, Vinca rosea

Cell-free extracts of $\text{Vinca rosea}$ seedlings exhibited enzyme activities for the following reactions: S-adenosyl-L-methionine (SAM) decarboxylation, spermidine synthesis from decarboxylated SAM and putrescine, and 5′-methylthioadenosine hydrolysis to 5-S-methyl-5-thio-D-ribose and adenine. SAM decarboxylation was stimulated by putrescine and inhibited by semicarbazide. The 15-fold purified ribohydrolase possessed a K_m of 1. 03 × 10^?5 M and a high specificity for 5′-methylthioadenosine.