CO2 production predicted from isocitrate dehydrogenase activity and bisubstrate enzyme kinetics in the marine bacterium Pseudomonas nautica

Abstract

ABSTRACT. COL product~on in aerobic bacteria was modeled from the time-courses of the 1x1 vitl-o activity of isocitrate dehydrogenase (IDH), bacterial protein, and the concentrat~on of the carbon source in the cultures. The model was based on the concept of bisubstrate control of the IDH reaction throughout the exponential, steady-state, and senescent phases of the cultures In the exponential phase, the measured rates of CO, production and the In vltro IDH actlvity were closely coupled, but in the senescent phase, they became uncoupled The In vltro IDH actlvity remained hlgh even after the culture's carbon source was exhausted, while the CO, production fell to low levels Based on the hypothesis that thls uncoupling was caused by ~n t e r n a l substrate limitation, 2 mathematical models incorporating a bisubstrate enzyme kinetics algorithm were constructed and tested. The models predicted the rate of CO2 production throughout the different phases of the cultures w~t h a n r2 greater than 0.84.

Impact of acetate, pyruvate, and physiological state on respiration and respiratory quotients in Pseudomonas nautica

“…They based this proposal on the strong theoretical link between IDH and other Krebs cycle decarboxylases and the physiological rate of CO2 production (Walsh & Koshland 1984). Furthermore, they supported their proposal by showing that IDH activity could be used to predict CO2 production rates in cultures of marine bacteria (Packard et al 1996a).…”

“…So, proxy methods must be used as Packard et al (1988) did in their calculations of oceanic CO2 production rates from respiratory electron transfer system (ETS) activity. In an attempt to avoid conversion of O2 consumption rates, which are involved when ETS activity is used, to CO, production rates, Berdalet et al (1995) and Packard et al (1996a) proposed the use of isocitrate dehydrogenase (IDH) activity as a direct measurement of the CO, production rates. They based this proposal on the strong theoretical link between IDH and other Krebs cycle decarboxylases and the physiological rate of CO2 production (Walsh & Koshland 1984).…”

Modeling physiological processes in plankton on enzyme kinetic principles

“…As a result, this conceptual model has limited use (Blasco et al, 1984). Considering what we know about enzyme reactions and previous studies of isocitrate dehydrogenase (IDH) and CO 2 production in bacteria (Packard et al, 1996b;Roy and Packard, 2001), we propose a more realistic mathematical and chemical representation of nitrate uptake. Rather than considering only nitrate limitation as we did in our original model (Packard et al, 1971a), the proposed model would consist of an enzyme kinetic expression based on bisubstrate limitation by [NADH] as well as [NO 3 ].…”

“…Although this concept has been applied to photosynthesis (Farquhar et al, 1980), its development here is based on the models of nitrate reduction in phytoplankton (Packard et al, 1971a), respiratory oxygen consumption (Packard et al, 1996a) and respiratory carbon dioxide production (Packard et al, 1996b;Roy and Packard, 2001). In one of the earlier applications, the physiological rate of O 2 consumption was calculated from respiratory electron transfer activity without the benefit of intracellular substrate measurements and Michaelis constants (Packard et al, 1996a).…”

“…The biochemical models presented here are designed to advance this approach by introducing equations based on multisubstrate enzyme kinetics. These models follow the equations designed to calculate phytoplankton nitrate uptake (Packard et al, 1971a), and bacterial respiration (Packard et al, 1996a;1996b;Roy and Packard, 2001) and are conceptually similar to Farquhar's photosynthetic model (Farquhar et al, 1980).…”