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. 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 for gluconolactonase activity is most likely Ca(2+) or Mg(2+). Mg(2+), Mn(2+) and Co(2+) are equally efficient for the hydrolysis of diisopropyl phosphorofluoridate. Optimum pH is 6.4. Cofactor biosynthesis; L-ascorbate biosynthesis via UDP-alpha-D-glucuronate pathway; L-ascorbate from UDP-alpha-D-glucuronate: step 3/4. Monomer. Detected in liver (at protein level). Hepatocytes and renal proximal tubular epithelium. In liver, the first peak of expression was found in 5-day-old neonates. Expression increases from day 7 and reaches a plateau at day 10. 3-6.5 moth-old adults express about a third the amount of neonates level. In kidney, expression increases from day 21 and reaches a maximal level at day 35, remains high until 3 months of age. The N-terminus is blocked. Belongs to the SMP-30/CGR1 family.