Reaction catalyzed by N-terminal E2 ubiquitin-conjugating enzyme (2.3.2.25)

	S-ubiquitinyl-[N-terminal E2 ubiquitin-conjugating E2 enzyme]-L-cysteine	+		[MDM2 protein]-N-terminal-amino acid	=		[N-terminal E2 ubiquitin-conjugating enzyme]-L-cysteine	+		N-ubiquitinyl-[ MDM2 protein]-N-terminal amino acid
	S-ubiquitinyl-[N-terminal E2 ubiquitin-conjugating E2 enzyme]-L-cysteine	+		[MDM2 protein]-N-terminal-amino acid	=		[N-terminal E2 ubiquitin-conjugating enzyme]-L-cysteine	+		N-ubiquitinyl-[ MDM2 protein]-N-terminal amino acid