ID 2.7.7.100 DE SAMP-activating enzyme. AN SAMP-activating enzyme E1. CA [small archaeal modifier protein]-C-terminal Gly-Gly + ATP + H(+) = CA [small archaeal modifier protein]-C-terminal Gly-Gly-AMP + diphosphate. CC -!- The enzyme catalyzes the activation of SAMPs (Small Archaeal Modifier CC Proteins), which are ubiquitin-like proteins found only in the CC Archaea, by catalyzing the ATP-dependent formation of a SAMP CC adenylate in which the C-terminal glycine of SAMP is bound to AMP via CC an acyl-phosphate linkage. CC -!- The product of this activity can accept a sulfur atom to form a CC thiocarboxylate moiety that acts as a sulfur carrier involved in CC thiolation of tRNA and other metabolites such as molybdopterin. CC -!- Alternatively, the enzyme can also catalyze the transfer of SAMP from CC its activated form to an internal cysteine residue, leading to a CC process termed SAMPylation (see EC 6.2.1.55). //