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Proteins are linear polymers of amino acids.

Although eukaryotic CPO has been reported to have an obligate requirement for molecular oxygen (Zagorec et al. ; Dailey ), S. cerevisiae still synthesizes 3–7% of its normal heme levels during anaerobic conditions, and oxygen is not an obligatory electron acceptor for heme synthesis during stress conditions in this organism (Hoffman et al. ).

Y. AsanoSyntheses of amino acids by new microbial enzymes (in Japanese), 66, 1117-1118 (1992).

A limitation of this approach has been the accessibility of only a restricted number of functional groups through the 20 amino acids in the genetic code.

Heme biosynthesis and degradation Flashcards | Quizlet

However, notable structural changes are observed at the proximal side of the heme cavity.

The liver is, at the same time, one of the organs with the highest rate of heme synthesis and the main body site deputed to the detoxification of heme coming from the bloodstream. We asked in which of these processes is FLVCR1a mainly involved. To address this point, we treated mice with the heme precursor ALA or with the hemolytic agent phenylhydrazine, to promote heme synthesis or heme recovery from the bloodstream, respectively.

Although we did not observe any difference after phenylhydrazine treatment (, ), increased heme content was found in the liver of Flvcr1afl/fl;alb-cre mice compared with Flvcr1afl/fl mice after ALA treatment, suggesting that on de novo synthesis, heme accumulated in the liver when FLVCR1a was absent (A). This resulted in a marked increase in the hepatic lipid peroxidation index (B). Interestingly, Flvcr1a was strongly induced by ALA treatment in the liver of Flvcr1afl/fl mice (C). On the other hand, the genes involved in heme and iron metabolism, such as Ho-1 and Fpn, were up-regulated to an higher extent in the liver of Flvcr1afl/fl;alb-cre mice than in that of Flvcr1afl/fl mice, and this was associated with a higher induction of the genes of the antioxidant response (C). Conversely, we observed a reduced expression of Alas1, Flvcr1b, and Tfr1 in the liver of Flvcr1afl/fl;alb-cre compared with Flvcr1afl/fl mice (C), suggesting an attenuation of the heme biosynthetic pathway in these animals. These results were confirmed in vitro on primary hepatocytes treated with ALA (DF; ).

Heme synthesis and degradation - SlideShare

In the liver, most of the newly synthesized heme is committed to CYP synthesis. To test whether FLVCR1a function is linked to heme synthesis stimulation on cytochromes induction, we treated our mice with inducers of 3 distinct classes of CYPs.

These data demonstrate that FLVCR1a is a heme exporter in hepatocytes that works in close association with the heme degradation pathway to maintain heme/iron homeostasis.

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Firstly, we injected mice with dexamethasone, an inducer of CYP3A. Dexamethasone treatment caused an increase in heme content in the liver of Flvcr1afl/fl;alb-cre mice, that was almost negligible in Flvcr1afl/fl counterpart (A). This effect was abrogated by co-treatment with the inhibitor of heme biosynthesis, succinylacetone (A). As a consequence of heme accumulation, a higher amount of lipid peroxides was generated on dexamethasone treatment in the liver of Flvcr1afl/fl;alb-cre mice compared with Flvcr1afl/fl mice (B). The analysis of gene expression demonstrated that Flvcr1a was induced in the liver of Flvcr1afl/fl mice after dexamethasone treatment, as occurred on ALA treatment (C). On the other hand, the heme-, iron-, and stress-related genes were induced to a higher extent in the liver of dexamethasone-treated Flvcr1afl/fl;alb-cre mice compared with the Flvcr1afl/fl counterpart (C–E), suggesting that the higher induction of these genes compensated for the lack of Flvcr1a. In addition, genes involved in heme biosynthesis, such as Alas-1, Flvcr1b, and Tfr1, were found to be significantly less expressed in Flvcr1afl/fl;alb-cre mice compared with Flvcr1afl/fl mice after dexamethasone treatment (F).


Data shown in C indicate that the enhanced HO activity was able to compensate for the lack of FLVCR1a to maintain heme content in the normal range on transient heme accumulation. This was further demonstrated by the analysis of gene expression. On heme treatment, Flvcr1afl/fl mice showed a strong induction of Flvcr1a in the liver, as well as an up-regulation of Ho-1, Fpn, H- and L-ferritin. Flvcr1afl/fl;alb-cre mice that were unable to induce Flvcr1a, showed a stronger induction of the heme degradation and iron storage/export pathways, as an attempt to compensate for the lack of heme export (E and F). This was not sufficient to control oxidative stress, as demonstrated by the significantly higher induction of the antioxidant genes in the liver of Flvcr1a-deleted mice after heme injection (E).

Host heme biosynthesis and degradation in schistosomiasis.

Similar results were obtained when mice were treated with benzo(a)pyrene (Be[a]P), an inducer of CYP1A1 and CYP1A2 (, ), and imidazole, an inducer of CYP2E1 (; ). Because the induction of Alas1 8h after Be(a)P injection was comparable in Flvcr1afl/fl;alb-cre and Flvcr1afl/fl (), the difference found at 16 hours post injection likely indicates that the heme biosynthetic pathway was switched off earlier in Flvcr1a-deleted mice than in its wild-type counterparts, as an attempt to compensate for the excess of heme accumulated in the liver.

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