Spiral Steroid Biosynthesis
Pathway for synthesis of steroid phosphoesters with 23 carbon atoms:
The enzymes for the addition of the two-carbon fragment are similar to the enzymes for lipid chain elongation. It remains to be determined, if there are separate enzymes for these substrates.
For every phosphocholine ester in bovine serum, a phosphoethanol-amine steroid ester was detected by LC-MS analysis in bovine adrenal extracts.
We propose that the phosphoethanolamine steroids are synthesized in the adrenal cortex and stored until needed. N-methylation, an ACTH-dependent process, would be required for secretion.
Chasalow F, Pierce-Cohen L. Ionotropin is the mammalian digoxin-like material (DLM). It is a phosphocholine ester of a steroid with 23 carbon atoms. Steroids. 136: 63-75 (2018). doi.org/10.1016/j.steroids.2018.03.001.
Avian (turkey) serum contains C339 with little, if any, C341, indicating it does not have an enzyme that can catalyze 5-dehydrosterol reductase (H) for 5-dehydropregnenolone phosphoesters.
Egg yolks from unfertilized eggs contain C313 in both the Na+ and K+ cation forms. There were small amounts of the spiral steroids, consistent with incomplete separation of yolks and whites.
Egg whites from unfertilized contain spiral steroids C337 and C339 but not C341. C361*, but not C363*, was also present. This pattern is consistent with the absence of 5-dehydrosterol reductase (H) that we observed in turkey serum.
Earlier, we noted that there was DLM in egg whites but not egg yolks. C337 and C339 are both spiral steroids. We do not yet have evidence that both of these compounds are DLM, but one of them must be.
There was no evidence for phosphoethanolamine steroid esters in the egg whites. Hence, the spiral steroids must be synthesized prior to formation of the eggshell.
The presence of both C339 and C361* in the egg white seems to suggest that these compounds have different functions.
Chasalow F. Spiral Phosphocholine Steroids and DLM in Chicken Eggs (). 8 (2019): 01-12. Doi: 10.31080/ecpe.2019.08.00593
Blue borders – existence confirmed by mass spectroscopy
Red borders – isolated to >90% homogeneity from serum
Black borders – proposed precursor or intermediate
A Phosphorylation enzyme E 20-23 Reduction
B N-Methylation F Ring Closure enzyme
C Condensation Reaction G 7-Dehydrosterol Reductase
D 20-23 Dehydration H 5-Dehydrosterol Reductase