Regulates glucokinase (GCK) by forming an inactive complex with this enzyme (PubMed:23621087, PubMed:23733961). 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:23621087, PubMed:23733961). 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. Found in liver and pancreas. Not detected in muscle, brain, heart, thymus, intestine, uterus, adipose tissue, kidney, adrenal, lung or spleen. Fructose 1-phosphate and fructose 6-phosphate compete for the same binding site. Genetic variations in GCKR define the fasting plasma glucose levels quantitative trait locus 5 (FGQTL5) [MIM:613463] (PubMed:18556336, PubMed:18678614). The normal fasting plasma glucose level is defined as less than 100 mg glucose per deciliter plasma (5.55 mmol per liter). Higher fasting plasma glucose levels predict type 2 diabetes in young adults and increases the risk of mortality (PubMed:18556336, PubMed:18678614). Belongs to the GCKR family.