GO:0102522:   tRNA 4-demethylwyosine alpha-amino-alpha-carboxypropyltransferase activity
Catalysis of the reaction: S-adenosyl-L-methionine + 4-demethylwyosine37 in tRNAPhe <=> 5"-S-methyl-5"-thioadenosine + H+ + 7-[(3S)-3-amino-3-carboxypropyl]-4-demethylwyosine37 in tRNAPhe