cytoplasman

Cytoplasman is a hypothetical term used in speculative cell biology to describe a membraneless, dynamic compartment that may exist within the cytoplasm of eukaryotic cells. In proposed models, it is a phase-separated condensate formed by multivalent interactions among cytosolic proteins and RNA molecules, with a size range that can vary from tens to hundreds of nanometers and a localization that commonly relates to the cytoskeleton.

Formation and properties are thought to arise through liquid-liquid phase separation. The condensate would be maintained by proteins with intrinsically disordered regions and modular interaction domains, and its assembly could be sensitive to cellular energy status, pH, ionic strength, and temperature. Under stress or metabolic shifts, cytoplasman might dissolve or reorganize, reflecting a responsive intracellular landscape.

Composition is described as diverse and cell-type dependent, potentially enriched for enzymes involved in glycolysis and nucleotide metabolism, RNA-binding proteins, chaperones, and various noncoding RNAs. Because the concept is still debated, reported compositions often vary between studies and experimental systems.

Possible functions attributed to cytoplasman include transient sequestration and co-localization of metabolic enzymes to coordinate flux through connected pathways, buffering of labile metabolites, protection of sensitive intermediates, and modulation of signaling networks by concentrating or excluding specific regulators.

Evidence for cytoplasman remains limited and controversial. Observations primarily rely on fluorescence imaging of tagged proteins and in vitro reconstitution, with concerns about artifacts and overexpression. Higher-resolution in vivo validation, including electron microscopy and genetic perturbation studies, is needed to establish whether cytoplasman is a distinct cellular entity or a theoretical construct.