Regulates glucokinase (GCK) by forming an inactive complex with this enzyme (PubMed:23957911). Acts by promoting GCK recruitment to the nucleus, possibly to provide a reserve of GCK that can be quickly released in the cytoplasm after a meal (PubMed:10456334). The affinity of GCKR for GCK is modulated by fructose metabolites: GCKR with bound fructose 6-phosphate has increased affinity for GCK, while GCKR with bound fructose 1-phosphate has strongly decreased affinity for GCK and does not inhibit GCK activity (PubMed:23957911). Interacts (fructose 6-phosphate bound form) with GCK. Under low glucose concentrations, GCKR associates with GCK and the inactive complex is recruited to the hepatocyte nucleus. Detected in liver (at protein level) (PubMed:7682971, PubMed:10518020). Not detected in muscle, brain, heart, testis, intestine or spleen (PubMed:10518020). Fructose 1-phosphate and fructose 6-phosphate compete for the same binding site. Belongs to the GCKR family.