SODIUM REQUIREMENT OF POLY-β-HYDROXYBUTYRIC ACID DEPOLYMERASE OF MICROCOCCUS HALODENITRIFICANS

Abstract

Cells of Micrococcus kalodenitrificans, a moderate halophile, contain poly-β-hydroxybutyric acid (PHBA), which is oxidized endogenously when cells are suspended in NaCl. The oxidation involves a depolymerase, a DPN-linked D(−)-β-hydroxybutyric acid (HBA) dehydrogenase, and the enzymes of the tricarboxylic acid cycle. Cells suspended in NaBr, Na₂SO₄, Li₂SO₄, and LiCl oxidize PHBA but cells suspended in KCl, KBr, K₂SO₄, MgCl₂, CaCl₂, CsCl, glucose, or glycerol, iso-osmotic with 0.4 molal NaCl or in water or buffers do not. Since cells washed with and resuspended in KCl do not oxidize their internal PHBA, it seems that nearly all the cell Na⁺ has been replaced by K⁺. These cells can be reactivated by the addition of Na⁺ or Li⁺, indicating that these ions are required for enzyme activity. In Na-depleted cells or their extracts the dehydrogenation of HBA and the oxidation of acetate are unimpaired, but there is no PHBA depolymerase activity. PHBA depolymerase can be reactivated by the addition of Na⁺. The results indicate that sodium or lithium salts readily penetrate the cells of M. halodenitrificans and are required to activate the PHBA depolymerase.