c-type cytochromes are characterized by the presence of two covalent bonds linking heme to apocytochrome and by the heme attachment motif in the apoprotein. Several molecular systems for the maturation of c-type cytochromes have evolved in different organisms. The best characterized are three of them: system I, system II and system III. Heme is synthesized in bacterial cytoplasm, in plastids, and in animal and fungal mitochondria. Therefore the maturation of bacterial and plastid c-type cytochromes involves the transport of heme and apocytochrome from the n-side to the p-side of the respective biological membranes and the formation of the covalent bond at the p-side. It should be underlined that the site of the c-type apocytochrome synthesis is also distinct from the site of its functioning. The aim of this review is to present the current state of knowledge concerning the structure and function of two systems – system I and system II – in the maturation of plant mitochondrial and plastid c-type cytochromes, respectively.
A high level of the nucleotide sequence conservation of mitochondrial nad3 and rps12 genes was found in four lupin species. The only differences concern three nucleotides in the Lupinus albusrps12 gene and three nucleotides insertion in the L. mutabilis spacer. Northern blot analysis as well as RT-PCR confirmed cotranscription of the luteus genes because the transcripts detected were long enough.
Purified cauliflower (Brassica oleracea var. botrytis) mitochondrial proteins fractionated into soluble, membrane, integral membrane and peripheral membrane samples were analyzed by 2D- PAGE (isoelectric focusing/ SDS polyacrylamide gel electrophoresis). 2D gels patterns were compared using the Imager Master 2D Elite software. 561 silver stained protein spots were resolved after electrophoresis under standard conditions of a whole protein extract. In the soluble fraction a prevalent number of more intense protein spots was observed. The cauliflower protein 2D patterns resembled Arabidopsis thaliana 2D patterns. The two protein spots selected which occupied a similar isoelectric point positions on both gels represented the same proteins as revealed by ESI-MS analysis of cauliflower proteins. The third selected spot belongs to unidentified proteins. The comparative analysis of mitochondrial suborganellar fractions proved the usefulness of this approach.
A high level of the nucleotide sequence conservation was found for mitochondrial nad3 gene of carrot. Three silent nucleotide substitutions differentiate nad3 open reading frames from cytoplasmic male sterile and male fertile carrots. All these differences are preserved on the RNA level. Partial and silent editing also distinguished both carrots. Three of the C to U conversions were specific to the fertile line. In the two examined carrot lines editing did not affect the mode of alteration of encoded amino acids.