Catalyzes the cleavage of L-arabino-gamma-lactone to L-arabonate. Is involved in a degradation pathway of L-arabinose that allows A.brasilense to grow on L-arabinose as a sole carbon source. Can also use D-galactono-1,4-lactone as substrate in vitro; however, the enzyme is probably not involved in the metabolism of D-galactose in vivo. H2O + L-arabinono-1,4-lactone = H(+) + L-arabinonate Binds 1 divalent metal cation per subunit. Belongs to the SMP-30/CGR1 family.