Biological complexes of poly-beta-hydroxybutyrate.

Short-chain complexed poly-beta-hydroxybutyrate, 130-170 monomer units, is a ubiquitous constituent of cells, wherein it is usually associated with other macromolecules by multiple coordinate bonds, or by hydrogen bonding and hydrophobic interactions. This conserved PHB has been isolated from the plasma membranes of bacteria, from a variety of plant tissues, and from the plasma membranes, mitochondria, and microsomes of animal cells. In bacterial membranes, PHB has been found complexed to the calcium salts of inorganic polyphosphates, and to single-stranded DNAs. The ability of PHB to solvate salts, consisting of cations having high solvation energies and large delocalized anions, is in accordance with its molecular characteristics, that of a flexible linear molecule possessing a large number of electron-donating ester oxygens suitably spaced to replace the hydration shell of cations. In turn, PHB may be rendered soluble in aqueous media by complexation to water-soluble proteins, such as serum lipoproteins and albumin. Such solvates are highly resistant to hydrolytic enzymes. These findings suggest that the physiological roles of this unique biopolymer may include the solvation of salts of polymeric anions to facilitate their movement through hydrophobic barriers, and the protection of cellular polymers from enzymatic degradation.