Jl. Mouget et al., INADEQUACY OF RUBISCO INITIAL AND TOTAL ACTIVITIES TO ACCOUNT FOR OBSERVED RATES OF PHOTOSYNTHETIC CARBON-DIOXIDE ASSIMILATION BY SCENEDESMUS-ECORNIS, European journal of phycology, 28(2), 1993, pp. 99-106
Both initial and total activity of ribulose-1,5, bisphosphate carboxyl
ase/oxygenase (Rubisco) measured for the green alga Scenedesmus ecorni
s are affected by the experimental procedure and they are not sufficie
ntly high to account for the rates of C-14 fixation by photosynthesis.
The very low beta-carboxylase activities detected (less than 3% of th
e Rubisco total activity) cannot explain the difference in CO2 fixatio
n. Attempts to obtain possible optimal conditions (pH, duration of act
ivation with Mg2+ and HCO3, absence of proteases, linearity of C-14 fi
xation with time) did not lead to increased activity yields. The subst
rate ribulose-1,5-bisphosphate was found to decrease the initial activ
ity at concentrations higher than 25 muM for algae harvested by centri
fugation and having thus experienced several minutes of darkness. Deac
tivation seems to be primarily responsible for this loss of activity.
Furthermore, initial and total activities decrease when the delay befo
re freezing increases, suggesting accumulation of an inhibitor from th
e light-dark transition metabolism during the first minutes of harvest
ing.