a b s t r a c tThe Antarctic bacterium Pseudoalteromonas haloplanktis encodes for a c-class carbonic anhydrase (CA, EC 4.2.1.1), which was cloned, purified and characterized. The enzyme (PhaCAc) has a good catalytic activity for the physiologic reaction of CO 2 hydration to bicarbonate and protons, with a k cat of 1.4 Â 10 5 s À1 and a k cat /K m of 1.9 Â 10 6 M À1 Â s À1 . A series of sulfonamides and a sulfamate were investigated as inhibitors of the new enzyme. Methazolamide and indisulam showed the best inhibitory properties (K I s of 86.7-94.7 nM). This contribution shed new light on c-CAs inhibition profiles with a relevant class of pharmacologic agents.Ó 2015 Elsevier Ltd. All rights reserved.Marine psychrophiles act as processors of the polar marine primary productivity constituting the base for the entire polar food web and, ultimately, feeding krill, fish, whales, penguins, and seabirds. 1,2 They play, in fact, a significant role in the so called 'substance turnover'. Moreover, a feature common to all psychrophiles are their remarkable ability to thrive under extremely cold and salty conditions. 3 Cold-adapted organisms have developed a number of adjustments at the molecular level to maintain metabolic functions at low temperatures, such as the production of enzymes, note as 'cold-enzyme'. 4-11 These enzymes are characterized by a specific activity at low and moderate temperatures higher than their mesophilic counterparts over a temperature range roughly covering 0-30°C and by a relative instability. 6,7,[11][12][13] Probably, in the case of psychrophilic microorganisms the selective pressure is essentially exerted towards the specific activity and not towards stability factors as happens in mesophilic or in thermophilic enzymes. The molecular structure of a 'cold-enzyme' is primarily characterized by an adequate plasticity of the molecule at the environmental temperature in order to accommodate the substrates with a minimum of energy expenditure. 14 'Cold-enzymes' naturally achieved a good compromise between activity and stability. There is a continuum in the adaptation of a protein to its environment. [4][5][6][7][8][9][10][11]13,[15][16][17][18][19][20][21][22] In fact, all known structural factors and weak interactions involved in protein stability are either reduced in number or modified in psychrophilic enzymes in order to increase their flexibility; but the same structural factors are also implicate for increasing the stability of the thermophilic proteins. [23][24][25][26][27][28][29] Carbonic anhydrases (CAs; EC 4.2.1.1) are metalloenzymes that catalyze CO 2 hydration to bicarbonate and protons. 4,5,[30][31][32][33][34][35][36][37][38] These enzymes are involved in a multitude of physiologic processes in organisms all over the phylogenetic tree, with six genetically distinct CA classes known to date: the a-, b-, c-, d-, f-and g-CAs. 26,[39][40][41][42][43][44][45][46][47][48][49][50] Their biochemical features are known in detail for at least four classes, together with their distribution and ...