Chrysolaminarin

Chrysolaminarin is a storage polysaccharide found in certain photosynthetic protists, notably chrysophyte algae (golden algae) and some diatoms. It serves as an energy reserve that accumulates in the cytoplasm and can be mobilized when light is scarce or conditions are unfavorable.

Structurally, chrysolaminarin is a β-D-glucan consisting primarily of glucose units linked by β-1,3-glycosidic bonds, with occasional β-1,6-linked side chains. The polymer varies in size among species, with chains comprising thousands of glucose units reported in some organisms. This composition distinguishes it from starch-based reserves and from other glucans in different algal lineages.

Occurrence and function: Chrysolaminarin is characteristic of Chrysophyceae and related heterokonts, where it often serves as the dominant storage carbohydrate, complementary to or replacing starch found in green algae. It provides a rapidly mobilizable glucose source during respiration or fermentation in dark or stress conditions.

Synthesis and degradation: The polymer is synthesized from UDP-glucose by specific β-1,3-glucosyltransferases. Degradation is mediated by β-1,3-glucanases, which release glucose for metabolic needs. Its solubility in hot water facilitates laboratory extraction and analysis.

Taxonomic and research relevance: The content and structure of chrysolaminarin can aid in the chemotaxonomic characterization of chrysophytes and diatoms. It is often contrasted with laminarin, the storage glucan of brown algae, because both are β-glucans with backbones of β-1,3 linkages and varying branching, yet they occur in different algal groups.