THEORETICAL FITTING OF ENERGETICS OF CAM PATH TO CALORIMETRIC DATA

The objective is to test fit of calorimetric data on Crassulacean acid metabolism (CAM) to current concepts in the field. Calculations, done by using maximum observed rates of nocturnal acid accumulation, and D elta H values for reactions in known processes of acid accumulation, w ere used to predict heat rates. The predicted heat rates were compared with heat rates measured by microcalorimetry. This investigation invo lved nine diverse species of CAM plants. In six species, calculated an d measured values were similar. Fitting the titratable acidity data to the microcalorimetric results, accounts for the expenditure of up to 7.5 molecules ATP per molecule of malate stored in vacuole. Of these 7 .5 ATP molecules, fitting suggests 3.5 are derived through the truncat ed glycolytic path of CAM and up to 4 ATP are generated through the pr ocessing of starch through to electron transport. This agrees with the general consensus, that in CAM at night, nocturnal fixation of CO2 in to malate and associated transport and storage functions are overwhelm ingly the dominant biochemical pathways and heat generating processes. Thus, in these six species, under our conditions, microcalorimetry is a valid measurement of nocturnal CO2 fixation and associated processe s. In three species calculated rates of heat evolved through known CAM pathways from measured nocturnal acid accumulation rates did not fit microcalorimetric measurements.