D-Proline: Comment to "An overview on D-amino acids".

An excellent 2017 review in this journal about D-amino acids by Genchi aims for a comprehensive representation of the current state of knowledge. Unfortunately, information about both D-proline and proline racemase is almost entirely missing. In our investigations into D/L-Pro-containing neuropeptides in cicadas, we have performed literature surveys in this context. Proline racemases in bacteria are known since 1957; their function has been studied mostly in prokaryotes and, more recently, proline racemase was identified in the unicellular eukaryotic parasite Trypanosoma cruzi. Published data on D-proline and/or proline racemase in other species are rare or non-existent.