Germinal proto-mitochondria from rat liver

Abstract

A number of properties of the smallest (less than 0.2 μm) germinal proto-mitochondria (PRMC) from rat liver have been studied. These PRMC were obtained by filtering the light fraction of hepatic mitochondria (MC) through calibrated millipore membranes. Germinal PRMC contain in general the same proteins as MC. However, they have the reduced content of flavoproteins and zero cytochrome oxidase. Germinal PRMC, in contrast to MC, almost does not contain the "aging pigment" - lipofuscin. They have DNA; the DNA/protein ratio in them is much higher than in MC, i.e. they are poor in protein. The obtained results support the earlier assumption that MC in specialized animal cells can arise from germinal PRMC - particles smaller than 0.2 μm containing DNA. It is assumed that the DNA molecules enter to cytoplasm during degradation of old MC serves as a seed for the formation of PRMC (with the connection of nuclear DNA).

Keywords: Flavoproteins; Lipofuscin; MC, mitochondria; Mitochondria; Mitochondrial DNA; PRMC, protomitochondria; Post-mitochondria; Proto-mitochondria; Respiratory chain.

Fig. 1

Optical microscopy of PRMC from rat liver obtained by filtration of the light fraction of MC through a millipore filter with a pore diameter of 0.2 μm, staining with Hoechst, in the regime of “fluorescence” (excitation - 350 nm; interference filter). Microscope Axio Imager.Z1, the lens EC Plan-Neofluar 100x/1.30 Oil Iris M27.

Fig. 2

Electrophoresis of proteins of PRMC <0.22 μm (right) and MC (center) in 10% polyacrylamide gel in the presence of 0.1% SDS, versus protein standards (left).

Fig. 3

Absorption spectra of cytochromes of MC (1) and PRMC <0.2 μm (2) after destruction of the suspension particles by detergent (0.5% SDS). Characteristic spectra are shown, minus light scattering.

Fig. 4

Flavin fluorescence spectra (excitation - 450 nm) of PRMC <0.2 μm (1) and MC (2) after destruction of the suspension particles by a detergent (0.5% SDS).

Fig. 5

Spectral characteristic of lipofuscin fluorescence (excitation at 360 nm) of PRMC <0.2 μm (1) and MC (2) after destruction of the suspension particles by detergent (0.5% SDS). The intensity at 490 nm belongs to the contribution from the flavin fluorescence band.

Fig. 6

UV absorption spectra of PRMC <0.2 μ (1) and MC (2) after destruction of the suspension particles by a detergent (0.5% SDS), as well as the difference spectrum (3). Characteristic spectra are shown, minus the residual light scattering.

Fig. 7

IR absorption spectra of the PRMC <0.22 μ (···) and MC (−).

Fig. 8

Scheme of the MC life cycle in specialized animal cells: 1 - aging of MC to post-MC, 2 - post-MC degradation to lipofuscin granules or 3- lysis of post-MC by proteases and lysosomes, 4 - DNA release (with some proteins) into cytoplasm, 5 - nucleation of a ~0.1-μm PRMC, 6 - synthesis of a number of membrane proteins, 7 - cooperation with nuclear DNA, synthesis of the majority of proteins and membrane formation, 8 - growth of PRMC, 9 - further growth and development of PRMC.