Lambda-carrageenase
Lambda-carrageenase is an enzyme which breaks down a polysaccharide found in red seaweeds, lambda-carrageenan. This enzyme has only been found in marine bacteria.
Two bacteria which produce lambda-carrageenase have been found. The marine bacterium Pseudoalteromonas carrageenovora strain ATCC 43555, which was isolated from sea water in Nova Scotia, and the deep-sea bacterial isolate Pseudoalteromonas sp. CL19, which was isolated from a sediment sample from Suruga Bay, Japan.
In both Alteromonas carrageenovora and Pseudoalteromonas sp. CL19, lambda-carrageenase is encoded by the cglA gene. The product of this gene is a protein consisting of 942 amino acids, this protein includes a 25 amino acid signal peptide. Lambda-carrageenase is found as a monomer. Its optimum pH for activity is 7.0, and optimum temperature is 35 °C. The enzyme specifically hydrolyses lambda-carrageenan, and is not active against iota- and kappa-carrageenans, agarose or porphyran.
Mechanism of action
Lambda-carrageenase cleaves the beta 1-4 glycosidic bonds in the linear backbone of lambda-carrageenan. This results in the formation of a tetrasaccharide: alpha-D-Galp2,6S--beta-D-Galp2S--alpha-D-Galp2,6S--D-Galp2S. This enzyme acts via a single displacement mechanism, causing an inversion of anomeric configuration of the substrate.