Transcriptional repressor of genes involved in glucosamine transport and utilization. Represses the expression of the gamAP operon by binding to the gamA-gamR intergenic region. Binding to DNA is allosterically inhibited by the effector glucosamine-6-phosphate (GlcN6P). N-acetylglucosamine-6-phosphate (GlcNAc6P) and glucose-6-phosphate (Glc6P) have no effect.