Question

Only the L-isomer is produced naturally, while racemic mixtures are produced synthetically and used commercially as food additives and energy supplements. So what happens when we consume D-malate? Does it just partake in the Krebs cycle, the citrate-malate/malate-aspartateshuttles, and such like the L-isomer? Or, does it just bioaccumulate and/or inhibit these processes? Until it gets excreted out?

Answer 1

D-malate might not be metabolized by the body as efficiently as L-malate due to the stereospecificity of enzymes and could be excreted or bioaccumulate until it is excreted. It does not contribute to the Krebs cycle like its counterpart, the L-isomer.

Step-by-step explanation:

When D-malate is consumed, it may not participate in the Krebs cycle or the citrate-malate/malate-aspartate shuttles like the L-isomer does, due to the stereospecific nature of enzymes. Enzymes such as malate dehydrogenase are designed to work with specific enantiomers, and (S)-malate, not its enantiomers like (R)-malate or D-malate, is the natural substrate for these enzymes.

Thus, D-malate may not be properly metabolized and could either be excreted unchanged or potentially interfere with metabolic processes. If D-malate is not metabolized, it may then be excreted or bioaccumulate until it can be removed from the body. This is unlike (S)-malate which is properly oxidized by malate dehydrogenase to form oxaloacetate, a crucial metabolite in the energy production cycle.

Enantiomers like D-malate, which do not naturally occur or are not utilized in human biochemistry, might thus present different pharmacological effects and may even be bioaccumulative depending on the substance's metabolic stability and the body's mechanisms for excretion.