Hydrolase with high substrate specificity for L-rhamnono-1,4-lactone. Catalyzes the second step in an alternative pathway for rhamnose utilization that does not involve phosphorylated intermediates. H2O + L-rhamnono-1,4-lactone = H(+) + L-rhamnonate Divalent metal cation. Inhibited by Zn(2+), Fe(2+) and Cu(2+), but not by EDTA. Part of gene cluster that contains the genes for this rhamnose catabolic pathway. Belongs to the metallo-dependent hydrolases superfamily.