Note on Coenzyme A Precursors: Pantothenic Acid vs. Pantethine

I've been meaning to mention that, in my opinion, pantethine is not superior to pantothenic acid (B5, vitamin B5) as a coenzyme A precursor. In my opinion, the cysteamine formed by the enzymatic hydrolysis of pantethine produces effects that are potentially problematic and undesirable. Some popular sources of information about pantethine give the impression that it is "closer" to coenzyme A than B5 is, but this isn't actually true. Pantethine is metabolized into B5 and cysteamine. Cysteamine is quite reactive, as I recall, and can then form mixed disulfides with a variety of different thiol groups on enzymes and other proteins, etc. For example, oral cysteamine was found to inhibit cholesterol biosynthesis in rabbits, but B5 did not reduce plasma cholesterol levels [Wittwer et al., 1987: (http://www.ncbi.nlm.nih.gov/pubmed/3689482)]. So it's pretty clear from that and other articles (http://scholar.google.com/scholar?num=100&hl=en&lr=&safe=off&q=pantethine+cysteamine+) that taking pantethine is basically like taking B5 and cysteamine or the disulfide form of cysteamine (cystamine). Also, cysteamine can inhibit the activity of the P-protein of the glycine cleavage system (GCS) [Fujiwara and Motokawa, 1983: (http://www.jbc.org/cgi/reprint/258/13/8156.pdf)(http://www.ncbi.nlm.nih.gov/pubmed/6863283?dopt=Abstract)] and thereby inhibit the overall activity of the GCS multienzyme complex [Hayasaka and Tada, 1983: (http://www.ncbi.nlm.nih.gov/pubmed/6679320); (http://scholar.google.com/scholar?num=100&hl=en&lr=&safe=off&q=cysteamine+%22glycine+cleavage%22)]. The fact that cysteamine can do that is not a good sign, in my opinion, for many reasons. Some cysteamine is formed endogenously during the turnover of coenzyme A, I think [it is: Dominy et al., 2007: (http://www.jbc.org/cgi/content/full/282/35/25189)(http://www.ncbi.nlm.nih.gov/pubmed/17581819?dopt=Abstract)], but the facts that cysteamine inhibits cholesterol biosynthesis in vivo, in rabbits, and that B5 does not would tend to suggest that the amounts of cysteamine formed endogenously, during CoA turnover, are small in comparison to the amounts derived from the hydrolysis of pantethine.