Degradation of glycinebetaine by betaine-homocysteine methyltransferase inAphanothece halophytica: Effect of salt downshock and starvation

We have investigated conditions leading to the degradation of glycinebetain e in Aphanothece halophytica and have shown the activity of betaine-homocys teine methyltransferase (BHMT). The intracellular glycinebetaine level was decreased approximately 50% after 36 h salt downshock from 2.0 M NaCl mediu m to 0.5 M NaCl medium. A slight additional decrease of glycinebetaine occu rred when salt downshock was combined with dark treatment. The omission of carbon and nitrogen sources in the growth medium further decreased intracel lular glycinebetaine. The activity of BHMT increased from 0 to 460 nmol h(- 1)mg(-1) after 3 h salt downshock. Higher strength of salt downshock result ed in higher activity of the enzyme. Small increase of the enzyme activity was also observed when A. halophytica was deprived of carbon and nitrogen s ources in the growth medium.