Chemical Properties, Distribution, and Physiology of Plant and Algal Carbonic Anhydrases

Abstract

Plant carbonic anhydrases (CAs) have a range of molecular weights (MW). Among flowering plants, dicotyledons with C3 photosynthesis have two isoenzymes of 140-250K each with 6 subunits, while monocotyledons have two isoenzymes of 42-45K. Plant and animal CAs have a similar amino acid content, subunit size and zinc content, suggesting they are homologous proteins, although the higher plant CAs have no esterase activity and are not strongly inhibited by sulfonamides. Algal CAs vary widely in MW and some are highly sensitive to sulfonamides like the animal enzymes. The two plant isoenzymes, from the chloroplast and cytosol, can be separated by gradient polyacrylamide gel electrophoresis and subsequently visualized by enzymic H+ ion production. In plants, CAs probably facilitate diffusion of CO2 to the site of photosynthetic fixation; they may also have a role in pH regulation, in the use of bicarbonate by aquatic plants and in concentrating inorganic carbon within the chloroplast.

Amino Acid Sequence Homology between N- and C-terminal Halves of a Carbonic Anhydrase in Porphyridium purpureum, as Deduced from the Cloned cDNA

“…However, we showed that one molecule of Porphyridium CA binds two zinc atoms, in contrast to other prokaryotic-type CAs which have been shown to bind one zinc atom per 2 S. Mitsuhashi et al, manuscript in preparation. molecule (2). Thus we rather expected that each half of Porphyridium CA binds one zinc atom and should exhibit CA activity.…”

“…In this connection, we recently found that in Porphyra (a multicellular red alga having a stellate chloroplast as in Porphyridium), polypeptide of a molecular mass of about 50 kDa cross-reacted with the antisera raised against the Porphyridium CA. 2 Three mammalian hexokinase isozymes (Types I, II, and III) are well characterized examples of the enzymes consisting of highly homologous N-terminal and C-terminal halves (e.g. Ref.…”

Malaria parasite carbonic anhydrase: inhibition of aromatic/heterocyclic sulfonamides and its therapeutic potential

“…The purified and native pfCA enzyme has a KI value of AZA higher than those of the human CA II and many bacterial CAs. Notably, the yeast CA, the plant CA and the mammalian CA III are peculiarly insensitive to AZA inhibition [60][61][62][63][64][65][66][67] .…”

Sequence of a cDNA Encoding Carbonic Anhydrase from Barley

“…Although its physiological function has not been clearly defined, it had been speculated that CA serves to concentrate CO, at the active site of Rubisco (Graham et al, 1984). However, recent work with transgenic plants expressing CA in the antisense orientation has shown that the enzyme does not play an essential role in carbon fixation, although the regulation of CA levels seems to parallel that of carboxylase Price et al, 1994).…”