AbstractsChemistry

Little is known regarding the catabolic mechanisms involved in the breakdown of glucose in mung bean (Phaseolus aureus) seedlings. Studies in other laboratories have shown that the TCA cycle pathway is operative in mung bean leaves, and have demonstrated the presence of enzymes for the oxidation of glucose to glucuronic acid in mung bean seedlings. In the present study, the primary pathways responsible for the catabolism of glucose in detached 10-13 day old mung bean shoots were identified and the relative participation of each of these pathways was estimated. The radiorespirometric method was employed for these experiments, using an ion chamber-electrometer system to monitor the respiratory ¹⁴CO₂ evolved from detached mung bean shoots catabolizing ¹⁴C-labeled glucose substrates in the dark. Substrates were administered in two different ways, i.e., by means of a one-dose method and a continuous feeding method. The one-dose experiments gave rise to respiratory ¹⁴CO₂ yield data which were used to estimate the relative pathway contributions. With the continuous feeding experiments, a metabolic steady state with regard to glucose utilization was realized, and the data on ¹⁴CO₂ production enabled one to calculate the catabolic rates of the individual glucose pathways. Comparison of the relative rates also provided one with information on the relative participation of glucose pathways. By use of both the yield method and the catabolic rate method, it was concluded that in mung bean (Phaseolus aureus) seedlings, glucose is catabolized mainly by way of the Embden- Meyerhof- Parnas pathway, and that the pentose phosphate pathway and the glucuronic acid pathway played minor roles in the overall catabolism of glucose.