DEPOLYMERIZATION OF POLY-β-HYDROXYBUTYRATE BY AN INTRACELLULAR ENZYME SYSTEM

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Abstract
Merrick, J. M. (State University of New York, Buffalo), and M. Doudoroff. Depolymerization of poly-β-hydroxybutyrate by an intracellular enzyme system. J. Bacteriol. 88:60–71. 1964.—The poly-β-hydroxybutyric acid contained in the “lipid granules” of Bacillus megaterium is hydrolyzed to d(−)-β-hydroxybutyric acid by a complex enzyme system present in the soluble enzyme fraction of polymer-depleted cells of Rhodospirillum rubrum. This system consists of a thermostable “activator,” a thermolabile “depolymerase,” and an “esterase.” Under certain conditions, the activator can be replaced by trypsin. Various chemical and physical treatments inactivate the “native lipid granules,” and make them unsuitable as a substrate for the digestive enzymes. This inactivation of the granules is often expressed in the extent rather than the rate of their digestion, and is not correlated with the destruction of the polymer-synthesizing enzymes associated with the granules. The principal product of depolymerase action is d(−)-β-hydroxybutyric acid, but small amounts of esterified products are also released. These are hydrolyzed by the esterase.