Transcriptional activator of the glcDEFGB operon which is associated with glycolate utilization, and encodes malate synthase G and the genes needed for glycolate oxidase activity (PubMed:8606183, PubMed:9880556). Also negatively regulates the transcription of its own gene (PubMed:9880556). Glycolate acts as an effector, but GlcC can also use acetate as an alternative effector (PubMed:9880556). Is constitutively expressed (PubMed:8606183). Is repressed by the presence of glycolate (PubMed:9880556). GlcC exerts an autogenous repression on its own gene (PubMed:9880556). Abolishes both glycolate oxidase and malate synthase G activities. Is unable to grow on glycolate as the sole source of carbon, in contrast to wild type.