Contains Zn2+. The enzyme catalyses the activation of SAMPs (Small Archaeal Modifier Proteins), which are ubiquitin-like proteins found only in the Archaea, by catalysing the ATP-dependent formation of a SAMP adenylate in which the C-terminal glycine of SAMP is bound to AMP via an acyl-phosphate linkage. The product of this activity can accept a sulfur atom to form a thiocarboxylate moiety that acts as a sulfur carrier involved in thiolation of tRNA and other metabolites such as molybdopterin. Alternatively, the enzyme can also catalyse the transfer of SAMP from its activated form to an internal cysteine residue, leading to a process termed SAMPylation (see EC 6.2.1.55, E1 SAMP-activating enzyme).
