Histidine, an essential amino acid, is primarily recognized for the biological activities of its L-enantiomer. However, the D-enantiomer, D-Histidine, is gaining attention in nutritional science for its distinct properties and potential applications that extend beyond the well-established functions of L-histidine.

While L-histidine is crucial for protein synthesis, neurotransmitter production (histamine), and immune function, D-Histidine, being biologically inactive in these typical pathways, presents an interesting case for study. Researchers are investigating its potential as a probe to understand metabolic pathways. By using D-Histidine, scientists can isolate the chemical effects of the imidazole side chain without the complex biological interactions of its L-counterpart. This allows for a clearer understanding of substrate specificity in enzymes and transporters. The D-Histidine nutritional science applications are thus rooted in its utility as a research tool.

Furthermore, the metabolic fate of D-Histidine is a subject of ongoing research. While it's not incorporated into proteins, it can be utilized by certain bacteria, such as Escherichia coli, in their metabolic processes, sometimes serving as a precursor for L-histidine synthesis. This bacterial metabolism of D-Histidine highlights inter-species metabolic pathways and could have implications in areas like gut microbiome research. Understanding these pathways is part of the broader exploration of D-Histidine metabolism.

The chelating properties of D-Histidine, similar to L-histidine, are also being explored in nutritional contexts. The ability to bind metal ions could influence nutrient absorption and metabolism. While L-histidine is known to play a role in iron and zinc transport, the independent effects of D-Histidine in these processes are being investigated. This could lead to new insights into mineral bioavailability and the design of fortified foods or supplements.

In essence, the study of D-Histidine in nutritional science is about understanding the subtle yet significant differences between enantiomers and leveraging these differences for research and potential applications. Its role is less about direct nutritional benefit and more about providing a unique chemical entity to dissect complex biological systems. The exploration of D-Histidine's metabolic pathways and its interaction with biological systems continues to reveal its potential value in scientific inquiry.