Inadequacy of Rubisco initial and total activities to account for observed rates of photosynthetic carbon dioxide assimilation byScenedesmus ecornis

Abstract

LOUIS LEGENDRE 3 ANDBoth initial and total activity of ribulose-l,5, bisphosphate carboxylase/oxygenase (Rubisco) measured for the green alga Scenedesmus ecornis are affected by the experimental procedure and they are not sufficiently high to account for the rates of ~4C fixation by photosynthesis. The very low fl-carboxylase activities detected (less than 3% of the Rubisco total activity) cannot explain the difference in CO2 fixation. Attempts to obtain possible optimal conditions (pH, duration of activation with Mg 2+ and HCO3, absence of proteases, linearity of 14C fixation with time) did not lead to increased activity yields. The substrate ribulose-l,5-bisphosphate was found to decrease the initial activity at concentrations higher than 25/IM for algae harvested by centrifugation and having thus experienced several minutes of darkness. Deactivation seems to be primarily responsible for this loss of activity. Furthermore, initial and total activities decrease when the delay before freezing increases, suggesting accumulation of an inhibitor from the light-dark transition metabolism during the first minutes of harvesting.

Variation in Rubisco and other photosynthetic parameters in the life cycle of Haematococcus pluvialis

“…These degrees of activation might be partly attributable to the instability of this enzyme. In kelp extract, temperature increase or long assay duration resulted in the rapid loss of Rubisco activity, which has been termed "fallover" (Gerard and Driscoll, 1996), and was described for green microalgae (Mouget et al, 1993). We have demonstrated that rbcL gene expression was at its maximum in the orange resting cells (Fig.2), illustrating higher CO 2 fixation potential in the orange and green resting cells.…”

PRELIMINARY INVESTIGATIONS INTO THE STRUCTURE AND ACTIVITY OF RIBULOSE BISPHOSPHATE CARBOXYLASE FROM TWO PHOTOSYNTHETIC DINOFLAGELLATES1

“…This rapid loss of carboxylase activity may well account for the 100-fold discrepancy between RuBPdependent COs fixation and the photosynthetic rate measured by oxygen evolution. It is well recognized that the measured concentration of Rubisco in algae does not explain the rate of photosynthesis, but there is usually no more than a 2or 3-fold difference (Mouget et al 1993).…”

Algal growth enhancement by bacteria: Is consumption of photosynthetic oxygen involved?

“…In preliminary experiments, the growth response of several microalgal and cyanobacterial species to bacteria was first examined on solid culture media using agar plate methods developed previously [14]. All subsequent experiments using liquid media were conducted with the green microalga S. bicellularis that was rendered axenic by serial transfers on solid medium [17]. The effect of bacteria or a bacterial culture supematant on the growth of microalgae was evaluated in liquid culture as follows: an axenic stock culture of S. bicellularis (cell density, ca.…”