Abstract
The γ-carbonic anhydrases (CAs, EC 4.2.1.1) present in the Antarctic marine bacteria Pseudoalteromonas haloplanktis and Colwellia psychrerythraea, herein referred to as PhaCA and CpsCA, respectively, were investigated for their activation with a panel of 24 amino acids and amines. Both bacteria are considered Antarctic models for the investigation of photosynthetic and metabolic pathways in organisms adapted to live in cold seawater. PhaCA was much more sensitive to activation by these compounds compared to the genetically related enzyme CpsCA. The most effective PhaCA activators were d-Phe, l-/d-DOPA, l-Tyr and 2-pyridyl-methylamine, with the activation constant KA values of 0.72–3.27 µM. d-His, l-Trp, d-Tyr, histamine, dopamine, serotonin anddicarboxylic amino acids were also effective activators of PhaCA, with KA values of 6.48–9.85 µM. CpsCA was activated by d-Phe, d-DOPA, l-Trp, l-/d-Tyr, 4-amino-l-Phe, histamine, 2-pyridyl-methylamine and l-/d-Glu with KA values of 11.2–24.4 µM. The most effective CpsCA activator was l-DOPA (KA of 4.79 µM). Given that modulators of CAs from Antarctic bacteria have not been identified and investigated in detail for their metabolic roles to date, this research sheds some light on these poorly understood processes.
Highlights
Pseudoalteromonas haloplanktis and Colwellia psychrerythraea are bacteria adapted to live in the extreme conditions of the Antarctic Ocean
In many organisms including bacteria, carbonic anhydrases (CAs) are the main players in pH homeostasis and related physiologic processes, which are involved in the metabolism, survival and colonization of various niches in which these organisms thrive [18,19,20,21,22,23,24,25]
As for all CA classes investigated so far, the activators of the γ-CAs participate in the catalytic cycle [35,36,37,38,39,40,41,42], most probably by facilitating the rate-determining step of the catalytic cycle (shown schematically by the ping-pong Reactions (1) and (2) below)
Summary
These marine heterotrophic bacteria are thought to rely on simplified metabolic strategies which evolved in order to overcome thermodynamic constraints connected toliving at low temperatures and in the dark for prolonged periods during the Antarctic winter [1,2,3,4,5,6,7]. CAs convert the neutral molecules CO2 and water to a weak base (bicarbonate) and a strong acid (hydronium ion) with very high efficacy [8,13] For this reason, in many organisms including bacteria, CAs are the main players in pH homeostasis and related physiologic processes, which are involved in the metabolism, survival and colonization of various niches in which these organisms thrive [18,19,20,21,22,23,24,25].
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