A theoretical study on the amount of ATP required for synthesis of microbial cell material

The amount of ATP required for the formation of microbial cells growing under various conditions was calculated. It was assumed that the chemical composition of the cell was the same under all these conditions. The analysis of the chemical composition of microbial cells of Morowitz (1968) was taken as a base. It was assumed that 4 moles of ATP are required for the incorporation of one mole of amino acid into protein. The amount of ATP required on account of the instability and frequent regeneration of messenger RNA was calculated from data in the literature pertaining to the relative rates of synthesis of the various classes of RNA molecules in the cell. An estimate is given of the amount of ATP required for transport processes. For this purpose it was assumed that 0.5 mole of ATP is necessary for the uptake of 1 g-ion of potassium or ammonium, and 1 mole of ATP for the uptake of 1 mole of phosphate, amino acid, acetate, malate etc. The results of the calculations show that from preformed monomers (glucose, amino acids and nucleic acid bases) 31.9 g cells can be formed per g-mole of ATP when acetyl-CoA is formed from glucose. When acetyl-CoA cannot be formed from glucose and must be formed from acetate, Y _ATP ^MAX is only 26.4. For growth with glucose and inorganic salts a Y _ATP ^MAX value of 28.8 was found. Addition of amino acids was without effect on Y _ATP ^MAX but addition of nucleic acid bases increased the Y _ATP ^MAX value to that for cells growing with preformed monomers. Under these conditions 15–20% of the total ATP required for cell formation is used for transport processes. Much lower Y _ATP ^MAX values are found for growth with malate, lactate or acetate and inorganic salts. During growth on these substrates a greater part of the ATP required for cell formation is used for transport processes. The calculated figures are very close to the experimental values found. The interrelations between Y _ATP ^MAX and Y_ATP, the specific growth rate (μ), the maintenance coefficient (m_e) and the P/O rate are given. From a review of the literature evidence is presented that these parameters may vary under different growth conditions. It is concluded that in previous studies on the relation between ATP production and formation of cell material these effects have unjustly been neglected.