6.2.1.55	ATP + [SAMP]-Gly-Gly + [E1 SAMP-activating enzyme]-L-cysteine = S-[[SAMP]-Gly-Gly]-[[E1 SAMP-activating enzyme]-L-cysteine] + AMP + diphosphate	
6.2.1.55	ATP + [SAMP]-Gly-Gly = diphosphate + [SAMP]-Gly-Gly-AMP	
6.2.1.55	[SAMP]-Gly-Gly-AMP + [E1 SAMP-activating enzyme]-L-cysteine = S-[[SAMP]-Gly-Gly]-[[E1 SAMP-activating enzyme]-L-cysteine] + AMP