The problem of the possible occurrence of silicon porphyrins in the living organisms has been put forward in the context of the hypothesis of siliceous life forms and the study of the molecular evolution of porphyrin systems. Some properties of the tetrapyrrole complexes of silicon as well as essential data and theories from domains of silicon biochemistry and paleobiochemistry have been reviewed.This has been a basis for doing some extrapolations and showing connections with bioelectronics, whereas some possible functions of (...) hypothetical Si-porphyrins in biostructures, e.g. catalytic ones, have been shown. In the bioplasma concept, a possible use of Si-tetrapyrrole complexes as a model useful in the study of the plasma mechanism of enzymatic catalysis has been proposed, and a role of silicon analogues of chlorophyll-like compounds in primordial photosynthesis has been suggested. (shrink)

In this article, David Shemin, who is now in retirement, describes how in 1944 he ingested 66 g of 15N‐labeled glycine in order to determine the half‐life of hemoglobin and other blood proteins. The ramifications of the experiment led to the unravelling of the biosynthesis of porphyrins and the role of glycine and α‐aminolevulinic acid in heme, vitamin B12 and chlorophyll synthesis.

Humans accumulate porphyrins in the body mostly during the course of porphyrias, diseases caused by defects in the enzymes of the heme biosynthesis pathway and that produce acute attacks, skin lesions and liver cancer. In contrast, some wild mammals and birds are adapted to accumulate porphyrins without injurious consequences. Here we propose viewing such physiological adaptations as potential solutions to human porphyrias, and suggest certain wild animals as models. Given the enzymatic activity and/or the patterns of porphyrin excretion (...) and accumulation, the fox squirrel, the great bustard and the Eurasian eagle owl may constitute overlooked models for different porphyrias. The Harderian gland of rodents, where large amounts of porphyrins are synthesized, presents an underexplored potential for understanding the carcinogenic/toxic effect of porphyrin accumulation. Investigating how these animals avoid porphyrin pathogenicity may complement the use of laboratory models for porphyrias and provide new insights into the treatment of these disorders. (shrink)