The second type of putative group translocators use nicotinamide ribonucleoside uptake porters (PnuC; 4.B.1) of bacteria. They use ATP as the phosphoryl donor and phosphorylate external nicotinamide ribonucleoide to give cytoplasmic nicotinamide mono nucleotide (NMN) plus ADP. Several predicted substrates of PnuC homologues suggest that at least some of these substrates are not phosphorlated during transport.