β-Poly(L-malate) production by Physarum polycephalum ¹³C: Nuclear magnetic resonance studies

Abstract

β-Poly(l-malate) (PMLA) production in Physarum polycephalum has been followed by using d-[1-13C]glucose and Ca13CO3. Nuclear magnetic resonance studies of PMLA showed that the 13C label from [1-13C]glucose was incorporated in the presence of CaCO3 into positions C-3 (-CH2-) and C-4 (-CO-) of the l-malate repeating unit of PMLA. The 13C label from Ca13CO3 was incorporated into position C-4 and indicated that not only the endogenous CO2 but also the exogenous CO2 from CaCO3 served significantly as a carbon source for PMLA production. In the absence of CaCO3, the 13C labeling pattern of PMLA from d-[1-13C]glucose was almost indistinguishable from that for the natural abundance 13C-NMR spectrum of the polymer. These results indicated that l-malate used for PMLA production is synthesized either via carboxylation of pyruvate and reduction of oxaloacetate in the presence of CaCO3 or via the oxidative tricarboxylic acid (TCA) cycle in the absence of CaCO3. Avidin strongly inhibited the formation of l-malate via carboxylation; the 13C labeling pattern of PMLA in the presence of CaCO3 was almost identical with that for the natural abundance spectrum when avidin was added, indicating that l-malate utilized for PMLA production was supplied under this condition by the oxidative TCA cycle.