Effect of Betaine on Enzyme Activity and Subunit Interaction of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase from Aphanothece halophytica

Abstract

The presence of betaine, a quaternary ammonium compound, at a concentration (0.5 molar) reported to accumulate inside Aphanothece halophytica in response to increasing external salinity, slightly promoted ribulose-1,5-bisphosphate (RuBP) carboxylase activity. KCI at 0.25 molar inhibited RuBP carboxylase about 55%. Betaine relieved the inhibition by 0.25 M KCI and the original uninhibited activity was restored at 1 M betaine. Other osmoregulatory solutes such as sucrose and glycerol also reduced KCI inhibition, though to a lesser extent than betaine. Proline had no effect. The protective effect of betaine against KCI inhibition of RuBP carboxylase activity was also observed in other cyanobacteria, i.e. Synechococcus ACMM 323, Plectonema boryanum, and Anabaena variabilis, and in the photosynthetic bacterium Rhodospirillum rubrum but not in Chromatium vinosum. Apart from betaine, other quaternary ammonium compounds, i.e. sarcosine and trimethylamine-N-oxide (TMAO), but not glycine, also protected the enzyme against KCI inhibition and the effectiveness of such compounds appeared to correlate with the extent of N-methylation. Heat and cold inactivation of the enzyme could be protected by either betaine or KCI. However, best protection occurred when both betaine and KCI were present together. The Km (CO2) was not altered by either betaine or KCI, nor when they were present together. However, the Km (RuBP) was increased about 5-fold by KCI, but was unaffected by betaine. The presence of betaine together with KCI lowered the KCI-raised Km (RuBP) by about half. The extent of the dissociation of the enzyme molecule under the condition of low ionic strength was reduced by either betaine or KCI alone and more so when they were present together. Glycine, sarcosine, and TMAO were more effective than betaine or KCI in lowering the extent of the dissociation of the enzyme molecule.

Preliminary Genetic Studies of the Phenotype of Betaine Deficiency in Zea mays L.

“…Betaine appears to be far less inhibitory to protein synthesis in vitro in comparison to inorganic ions of equivalent concentration (1, 4), and this type of evidence supports the notion that betaine accumulation is more compatible with cytoplasmic functions than accumulation of inorganic ions as cytoplasmic osmotica (27). Glycinebetaine is reported to have stabilizing effects on proteins at high temperatures (12,18).…”

Is glycine betaine a non‐compatible solute in higher plants that do not accumulate it?

“…These compounds should, by definition, be non-toxic at high concentrations to cytoplasmic functions (Wyn Jones & Storey 1981), allowing turgor maintenance and/or protection of macromolecular structures (e.g protein folding or membrane stability) against the destabilizing effect of the decrease in water activity (Stewart & Lee 1974). Nevertheless, this 'protection' concept is essentially based on indirect evidence from in vitro experiments, such as the recovery of catalytic activities of enzymes inhibited by NaCl (Incharoensakdi, Takabe & Akazawa 1986;Solomon etal. 1994).…”

“…the destabilizing effects of chaotropic agents such as NaCl (Manetas 1990) or KCl (Incharoensakdi, Takabe & Akazawa 1986) as well as against thermal inactivation (Nikolopoulos & Manetas 1991;Arakawa & Timasheff 1985). However, these kinds of experiment do not integrate the functions of membranous systems, especially those concerned with the transduction of energy in chloroplasts and mitochondria.…”

Isolation and Functional Characterization ofN-Methyltransferases That Catalyze Betaine Synthesis from Glycine in a Halotolerant Photosynthetic Organism Aphanothece halophytica

“…halophytica is an oxygen-evolving halotolerant cyanobacterium that can grow in a wide range of salinity conditions from 0.25 to 3.0 M NaCl concomitant with the accumulation of betaine (14,20). Previous studies have shown that A. halophytica has unique systems to survive under severe environmental conditions (20 -24).…”

“…Previous studies have shown that A. halophytica has unique systems to survive under severe environmental conditions (20 -24). Ribulose-1,5-bisphosphate carboxylase/oxygenase of A. halophytica dissociates easily into large and small subunits when betaine was absent (20). A. halophytica DnaK has been shown to contain the longer C-terminal segment than other DnaK/Hsp70 family members (21) and exhibit extremely high protein folding activity at high salinity (22).…”