CARBONIC-ANHYDRASE IN THE MARINE DIATOM THALASSIOSIRA-WEISSFLOGII (BACILLARIOPHYCEAE)

The zinc metalloenzyme carbonic anhydrase plays a critical role in ino rganic carbon acquisition in marine diatoms, thus conferring on zinc a key role in oceanic carbon cycling As a first step in determining the location and function of carbonic anhydrase (CA) in Bacillariophyceae , we purified and partially sequenced CA front T. weissflogii (Gru) Fr yxell et Hasle (TWCA1) and cloned the corresponding cDNA (twcal). The twcal sequence is different from other known algal carbonic anhydrase genes, and en codes a protein of roughly 34 kDa. The amino terminal am ino acids sequenced from purified TWCA1 are 72 residues downstream of the putative starting methionine predicted by twca1. This difference m ay be due to the presence of a short-lived signal sequence designed to guide the enzyme to the correct cellular location. The absence of any homology between TWCA1 and previously sequenced CAs from Chlorophycea e may indicate either convergent evolution or that carbon acquisition represents a fundamental physiological difference among algal phyla.