Malate metabolism

Ruffner, H. P., Hawker, J. S., and Hale, C. R. (1976). Temperature and enzymic control of malate metabolism in berries of Vitis vinifera. Phytochemistry 15,1877-1880. 

FIG. 4.2 Malate metabolism in mitochondria from body wall muscle of adult Ascaris smm. (1) Fumarase (2) malic enzyme (3) pyruvate dehydrogenase complex (4) complex I (5) succinate-coenzyme Q reductase (complex II, fumarate reductase) (6) acyl CoA transferase (7) methylmalonyl CoA mutase (8) methyl-malonyl CoA decarboxylase (9) propionyl CoA condensing enzyme (10) 2-methyl acetoacetyl CoA reductase (11) 2-methyl-3-oxo-acyl CoA hydratase (12) electron-transfer flavoprotein (13) 2-methyl branched-chain enoyl CoA reductase (14) acyl CoA transferase. 

We can conclude that CAM plants do have photorespiration in that glycolate is produced in the light, RudP carboxylase has oxygenase activity, there is a postillumination CO2 burst, and O2 inhibits photosynthesis. Dissimilarities between these photorespiratory features and photorespiration in C3 plants are most likely due to the gas exchange phenomena centered around malate metabolism. 

There are numerous reports in the literature of a depression in daytime CO2 uptake in non-CAM plants (see Stocker, 1960 Larcher, 1973). The occurrence of noon depression of photosynthesis (Stocker, 1960) seems to be especially common in plants growing in arid habitats, the same habitats in which CAM plants exist. However, there is a fundamental difference between the noon depression of CO2 uptake in CAM and non-CAM plants. In species without CAM, the depression is caused by stress factors such as temporary water deficit, high air temperature, or reduced atmosphere moisture. These factors cause stomata closure during midday, thus inhibiting photosynthesis. In CAM plants, however, the occurrence of the CO2 uptake depression is an essential consequence of malic acid metabolism which characterizes CAM (Kluge, 1968 b). For example, in CAM plants the depression occurs independently of the actual water status of the leaves, i.e., it occurs in nonstressed plants as well as stressed. An explanation of the coupling between malate metabolism of CAM and the daytime closure of the stomata in CAM plants is suggested in Chapter 5.3.2.2. 

Cappello, M.S., Stefani, D., Grieco, F., et al. (2008) Genotyping by amplified fragment length polymor[4iism and malate metabolism performances of indigenous Oenococcus oeni strains isolated from Primitivo wine, bit J Food Microbiol 127, 241-245. 

Acid-catalyzed hydration of isolated double bonds is also uncommon in biological pathways. More frequently, biological hydrations require that the double bond be adjacent to a carbonyl group for reaction to proceed. Fumarate, for instance, is hydrated to give malate as one step in the citric acid cycle of food metabolism. Note that the requirement for an adjacent carbonyl group in the addition of water is the same as that we saw in Section 7.1 for the elimination of water. We ll see the reason for the requirement in Section 19.13, but might note for now that the reaction is not an electrophilic addition but instead occurs... 

How many absorptions would you expect (S)-malate, an intermediate in carbohydrate metabolism, to have in its 1H NMR spectrum Explain. 

Theoretically, a fall in concentration of oxaloacetate, particularly within the mitochondria, could impair the ability of the citric acid cycle to metabolize acetyl-CoA and divert fatty acid oxidation toward ketogenesis. Such a fall may occur because of an increase in the [NADH]/[NAD+] ratio caused by increased P-oxida-tion affecting the equilibrium between oxaloacetate and malate and decreasing the concentration of oxaloacetate. However, pyruvate carboxylase, which catalyzes the conversion of pyruvate to oxaloacetate, is activated by acetyl-CoA. Consequently, when there are significant amounts of acetyl-CoA, there should be sufficient oxaloacetate to initiate the condensing reaction of the citric acid cycle. 

Stolz A, H-J Knackmuss (1993) Bacterial metabolism of 5-aminosalicylic acid enzymatic conversion to malate, pyruvate and ammonia. J Gen Microbiol 139 1019-1025. 

E. Martinoia and D. Rentsch, Malate compartmentation—Responses to a complex metabolism. Annu. Rev. Plant Physiol. Plant Mol. Biol. 45 441 (1994). 

Poly(L-malate) [poly(malic acid) (PMA)], is a water-soluble polyanion produced by slime molds and some yeasts such as Physarum polycephalum or Aureobasidium pullulans, respectively. Its function and metabolism has been studied during the last few years [122-125]. Recently, several PMA-degrad-ing bacteria have been isolated, and a cytoplasmic membrane-bound PMA hydrolase was purified from Comamonas acidovans strain 7789 [126] that... 

THE MALATE-ASPARTATE SHUTTLE HAS A KEY ROLE IN BRAIN METABOLISM 541... 

The malate-aspartate shuttle has a role in linking metabolic pathways in brain 542... 

Cheeseman, A. J. and Clark, J. B. Influence of the malate-aspartate shuttle on oxidative metabolism in synaptosomes. /. Neurochem. 50 1559-1565,1988. 

Examples of such intra cellular membrane transport mechanisms include the transfer of pyruvate, the symport (exchange) mechanism of ADP and ATP and the malate-oxaloacetate shuttle, all of which operate across the mitochondrial membranes. Compartmentalization also allows the physical separation of metabolically opposed pathways. For example, in eukaryotes, the synthesis of fatty acids (anabolic) occurs in the cytosol whilst [3 oxidation (catabolic) occurs within the mitochondria. 

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