Proakrosomaalivakuolit

Proakrosomaalivakuolit is a proposed vacuole-like organelle described in speculative biology as a membrane-bound compartment within certain prokaryote-like microbes and early-diverging eukaryotes. The name combines elements referring to primitive cellular forms (pro-), soma (body), and vakuol (vacuole). In the concept, the organelle would have a boundary that separates a lumen from the cytoplasm and may be enclosed by a lipid membrane or a proteinaceous shell, enabling the localization of specific enzymes, substrates, or storage products.

Structure and biogenesis: The boundary is hypothesized to arise by invagination or budding of the plasma membrane or by assembly of a protein shell around cytosolic contents. The lumen is proposed to contain osmolytes, metabolites, and sometimes hydrolytic enzymes for localized processing, while the surrounding cytoplasm maintains metabolic exchange through selective transport.

Function and roles: Proposed functions include osmotic regulation, sequestration of reactive intermediates, nutrient storage, and the compartmentalization of certain metabolic steps to increase efficiency or protect the cell from harmful intermediates.

Evolutionary context and distribution: The existence of proakrosomaalivakuolit is currently hypothetical, with unclear phylogenetic distribution. Some accounts place the concept in discussions of primitive endomembrane systems or novel archaeal adaptations, though independent validation is lacking.

Evidence and reception: Critics point to a lack of unambiguous molecular markers and potential artefacts in electron micrographs. The term remains controversial, and robust identification would require genetic or proteomic signatures unique to the organelle.

See also: carboxysomes, magnetosomes, and primitive endomembrane compartments.