6.2.1.45	ATP + ubiquitin + [ubiquitin-activating enzyme Uba5]-L-cysteine	the catalytic cysteine residue of isoform Uba5 is part of the adenylation domain in a alpha-helical motif	AMP + diphosphate + [ubiquitin-activating enzyme Uba5]-S-ubiquitinyl-L-cysteine	-	?	428402	
6.2.1.45	ATP + ubiquitin + [ubiquitin-activating protein E1]-L-cysteine	a carboxylgroup is first activated as an adenylate followed by its direct transfer to an autonomous molecular moiety in a single enzymatic step	AMP + diphosphate + [ubiquitin-activating protein E1]-S-ubiquitinyl-L-cysteine	-	?	425987	
6.2.1.45	ATP + ubiquitin + [ubiquitin-activating protein E1]-L-cysteine	-	AMP + diphosphate + [ubiquitin-activating protein E1]-S-ubiquitinyl-L-cysteine	-	?	425987	
6.2.1.45	ATP + ubiquitin + [ubiquitin-activating protein Uba1a]-L-cysteine	-	AMP + diphosphate + [ubiquitin-activating protein Uba1a]-S-ubiquitinyl-L-cysteine	-	?	428404	
6.2.1.45	ATP + ubiquitin + [ubiquitin-activating protein UBA1]-L-cysteine	enzyme forms higher molecular mass intermediates with ubiquitin	AMP + diphosphate + [ubiquitin-activating protein UBA1]-S-ubiquitinyl-L-cysteine	the enzyme-ubiquitin intermediates dissociate in presence of 2-mercaptoethanol, indicating thiolester linkage	?	428405	
6.2.1.45	ATP + ubiquitin + [ubiquitin-activating protein UBA2]-L-cysteine	enzyme forms higher molecular mass intermediates with ubiquitin	AMP + diphosphate + [ubiquitin-activating protein UBA2]-S-ubiquitinyl-L-cysteine	the enzyme-ubiquitin intermediates dissociate in presence of 2-mercaptoethanol, indicating thiolester linkage	?	428406	
6.2.1.45	ATP + ubiquitin + [ubiquitin-activating protein Uba6]-L-cysteine	isoform Uba6 forms a covalent link with ubiquitin in vitro and in vivo, which is sensitive to reducing conditions. Recombinant E1 enzyme Uba6 can activate ubiquitin and transfer it onto the ubiquitin-conjugating enzyme UbcH5B. Ubiquitin activated by Uba6 can be used for ubiquitylation of p53 and supports the autoubiquitylation of the E3 ubiquitin ligases HectH9 and E6-AP	AMP + diphosphate + [ubiquitin-activating protein Uba6]-S-ubiquitinyl-L-cysteine	-	?	428408	
6.2.1.45	ATP + ubiquitin + [ubiquitin-activating protein UBE1]-L-cysteine	-	AMP + diphosphate + [ubiquitin-activating protein UBE1]-S-ubiquitinyl-L-cysteine	-	?	428409	
6.2.1.45	ATP + ubiquitin fold modifier1 + [ubiquitin-activating enzyme Uba5]-L-cysteine	the catalytic cysteine residue of isoform Uba5 is part of the adenylation domain in a alpha-helical motif	AMP + diphosphate + [ubiquitin-activating enzyme Uba5]-S-(ubiquitin fold modifier1)-L-cysteine	-	?	428410	
6.2.1.45	ATP + ubiquitin mutant G76A + [ubiquitin-activating protein E1]-L-cysteine	-	AMP + diphosphate + [ubiquitin-activating protein E1]-S-(ubiquitin mutant G76A)yl-L-cysteine	mutant ubiquitin G76A, bearing a Gly to Ala substitution at the COOH terminus is a substrate for El enzyme. Ubiquitin G76A supports PPI-ATP exchange with 500fold decrease in kcat/Km compared to wild-type ubiquitin, does not produce detectable AMP-Ub with native El, produces stoichiometric AMP-Ub with thiol-blocked El, gives a stoichiometric burst of ATP consumption with either native or thiol-blocked El, support El-ubiquitin thiol ester formation with native El, and supports several downstream reactions of the proteolytic pathway with a 20% decrease to the rate of wild type ubiquitin	?	428411