Gluconolactonase with low activity towards other sugar lactones, including gulonolactone and galactonolactone. Catalyzes a key step in ascorbic acid (vitamin C) biosynthesis. Can also hydrolyze diisopropyl phosphorofluoridate and phenylacetate (in vitro). Calcium-binding protein. Modulates Ca(2+) signaling, and Ca(2+)-dependent cellular processes and enzyme activities (By similarity). D-glucono-1,5-lactone + H2O = D-gluconate + H(+) Binds 1 divalent metal cation per subunit. Most active with Zn(2+) and Mn(2+) ions. The physiological cofactor is most likely Ca(2+) or Mg(2+). Cofactor biosynthesis; L-ascorbate biosynthesis via UDP-alpha-D-glucuronate pathway; L-ascorbate from UDP-alpha-D-glucuronate: step 3/4. Monomer. Mainly present in the liver. Weak expression was found in the brain, lung and kidney. Protein amounts in liver decrease significantly with age. By calcium. Mice do not thrive after weaning when kept on a vitamin C-less diet. They develop scurvy, have reduced bone mineral density and brittle bones. Hepatocytes exhibit accumulation of lipid droplets. Mice display increased mortality after about 3 months, and their life span is shorter than normal. Belongs to the SMP-30/CGR1 family.