PubMed · 4300191
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H R Wulff. 1967-02-09. [Enzyme histochemistry. An introduction].. https://pubmed.ncbi.nlm.nih.gov/4300191/
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COXFA4L3 is a testis-specific cytochrome c oxidase subunit that enhances mitochondrial complex IV activity during spermatogenesis. From the analysis of Coxfa4l3 knockout mice, the isoform switch from COXFA4 to COXFA4L3 may increase the potential COX activity, although this activity does not appear in the testis. This latent enhancement becomes evident in sperm, where COXFA4L3 promotes higher respiratory capacity, increasing sperm motility and ATP production. These findings indicate that COXFA4L3 is a key regulator of mitochondrial energy metabolism and may provide insights into the mechanisms underlying male infertility.
Genetic studies indicate that hereditary susceptibility of the inner ear to aminoglycoside antibiotic toxicity is caused by a nucleotide 1555 A-to-G mutation in the mitochondrial 12S rRNA gene. Although the phenotype associated with this mutation is nonsyndromic hearing loss, the possibility remains that there could be effects on other tissues that, like the inner ear, contain numerous mitochondria, particularly muscle. We obtained a temporalis muscle specimen from a deaf patient with the A1555G mutation and found informative pathologic features, including mosaic activity of cytochrome c oxidase immunoreactivity and mitochondrial ultrastructure. These findings suggest that mitochondrial dysfunction from the A1555G mutation extends beyond the inner ear.
Mutants that decouple the proton pump of cytochrome c oxidase from Rhodobacter sphaeroides are postulated to do so by increasing the pK(a) of glutamate 286, which is 20 Angstrom away. The possibility that a conformational change near E286 is induced by the decoupling mutations (N139D and N207D) was investigated by FTIR difference spectroscopy. In both decoupled mutants, the reduced-minus-oxidized FTIR difference spectra show a shift of 2 cm(-1) to lower frequency of the band resulting from the absorbance of E286 in the oxidized enzyme. The decoupling mutants may influence E286 by altering the chain of water molecules which runs from the site of the mutations to E286.