Biomaterial Database

Biogenesis of cytochrome c in Neurospora crassa. Synthesis of apocytochrome c, transfer to mitochondria and conversion to Holocytochrome c. 1978

H Korb, and W Neupert

1. Precipitating antibodies specific for apocytochrome c and holocytochrome c, respectively, were employed to study synthesis and intracellular transport of cytochrome c in Neurospora in vitro. 2. Apocytochrome c as well as holocytochrome c were found to be synthesized in a cell-free homogenate. A precursor product relationship between the two components is suggested by kinetic experiments. 3. Apocytochrome c synthesized in vitro was found in the post-ribosomal fraction and not in the mitochondrial fraction, whereas holocytochrome c synthesized in vitro was mainly detected in the mitochondrial fraction. A precursor product relationship between postribosomal apocytochrome c and mitochondrial holocytochrome c is indicated by the labelling data. In the microsomal fraction both apocytochrome c and holocytochrome c were found in low amounts. Their labeling kinetics do not subbest a precursor role of microsomal apocytochrome c or holocytochrome c. 4. Formation of holocytochrome c from apocytochrome c was observed when postribosomal supernatant containing apocytochrome c synthesized in vitro was incubated with isolated mitochondria, but not when incubated in the absence of mitochondria. The cytochrome c formed under these conditions was detected in the mitochondria. 5. Conversion of labelled apocytochrome c synthesized in vitro to holocytochrome c during incubation of a postribosomal supernatant with isolated mitochondria was inhibited when excess isolated apocytochrome c, but not when holocytochrome c was added. 6. The data presented are interpreted to show that apocytochrome c is synthesized on cytoplasmic ribosomes and released into the supernatant. It is suggested that apocytochrome c migrates to the inner mitochondrial membrane, where the heme group is covalently linked to the apoprotein. The hypothesis is put forward that the concomitant change in conformation leads to trapping of holocytochrome c in the membrane. The problems of permeability of the outer mitochondrial membrane to apocytochrome c and the site and nature of the reaction by which the heme group is linked to the apoprotein are discussed.

UI	MeSH Term	Description	Entries
D008928	Mitochondria	Semiautonomous, self-reproducing organelles that occur in the cytoplasm of all cells of most, but not all, eukaryotes. Each mitochondrion is surrounded by a double limiting membrane. The inner membrane is highly invaginated, and its projections are called cristae. Mitochondria are the sites of the reactions of oxidative phosphorylation, which result in the formation of ATP. They contain distinctive RIBOSOMES, transfer RNAs (RNA, TRANSFER); AMINO ACYL T RNA SYNTHETASES; and elongation and termination factors. Mitochondria depend upon genes within the nucleus of the cells in which they reside for many essential messenger RNAs (RNA, MESSENGER). Mitochondria are believed to have arisen from aerobic bacteria that established a symbiotic relationship with primitive protoeukaryotes. (King & Stansfield, A Dictionary of Genetics, 4th ed)	Mitochondrial Contraction,Mitochondrion,Contraction, Mitochondrial,Contractions, Mitochondrial,Mitochondrial Contractions
D009491	Neurospora	A genus of ascomycetous fungi, family Sordariaceae, order SORDARIALES, comprising bread molds. They are capable of converting tryptophan to nicotinic acid and are used extensively in genetic and enzyme research. (Dorland, 27th ed)	Neurosporas
D009492	Neurospora crassa	A species of ascomycetous fungi of the family Sordariaceae, order SORDARIALES, much used in biochemical, genetic, and physiologic studies.	Chrysonilia crassa
D003574	Cytochrome c Group	A group of cytochromes with covalent thioether linkages between either or both of the vinyl side chains of protoheme and the protein. (Enzyme Nomenclature, 1992, p539)	Cytochromes Type c,Group, Cytochrome c,Type c, Cytochromes
D005779	Immunodiffusion	Technique involving the diffusion of antigen or antibody through a semisolid medium, usually agar or agarose gel, with the result being a precipitin reaction.	Gel Diffusion Tests,Diffusion Test, Gel,Diffusion Tests, Gel,Gel Diffusion Test,Immunodiffusions,Test, Gel Diffusion,Tests, Gel Diffusion
D001051	Apoenzymes	The protein components of enzyme complexes (HOLOENZYMES). An apoenzyme is the holoenzyme minus any cofactors (ENZYME COFACTORS) or prosthetic groups required for the enzymatic function.	Apoenzyme
D013347	Subcellular Fractions	Components of a cell produced by various separation techniques which, though they disrupt the delicate anatomy of a cell, preserve the structure and physiology of its functioning constituents for biochemical and ultrastructural analysis. (From Alberts et al., Molecular Biology of the Cell, 2d ed, p163)	Fraction, Subcellular,Fractions, Subcellular,Subcellular Fraction