Synthesis and Degradation of Carbonic Anhydrase in a Synchronized Culture of Chlamydomonas reinhardtii

The biosynthesis and degradation of carbonic anhydrase (CA;EC 4.3.1.1 [EC] ) was investigated during the course of synchronousculture of the unicellular green alga Chlamydomonas reinhardtii,carried out under a regime of 12 h of light and 12 h of darknesswith bubbling of ordinary air. The enzymatic activity increasedlinearly during the light phase. A coordinate increase in thelevel of the 35-kDa mature CA polypeptide was demonstrated byimmunostaining after poly-acrylamide gel electrophoresis andWestern blotting. Pulse-labeling with [¹⁴C]arginine followedby immunoprecipitation showed that the biosynthesis of the CApolypeptide is very active in the early light phase and rapidlydecreases after the middle of the light phase, indicating thatthe bio-synthetic activity does not reflect the quantity ofenzyme protein or the level of enzymatic activity. The 42-kDaprecursor but not the 35-kDa mature polypeptide was synthesizedin the dark. The 35-kDa polypeptide, pulse-labeled at the beginningof the light phase, was gradually degraded throughout the lightphase while it appeard to be stable in the dark. These resultssuggest that the messenger RNA coding for CA is present butits translation is limited in the dark. Normal translation ofmRNA and processing of the precursor to yield the holoenzymemay both require light. ¹Present address: Plant Laboratory, Kirin Brewery Co., Ltd.,Kitsuregawa-machi, Shioya-gun, Tochigi-ken, 329-314 Japan. (Received August 22, 1988; Accepted March 9, 1989)