the most metabolic activity in the cell occurs at cristae of the mitochondria.
the most metabolic activity in the cell occurs at cristae of the mitochondria.
where does the most metabolic activity in the cell occur?
cristae of the mitochondria
tetrazolium dye reduction is generally assumed to be dependent on nad(p)h-dependent oxidoreductase enzymes largely in the cytosolic compartment of the cell. therefore, reduction of mtt and other tetrazolium dyes depends on the cellular metabolic activity due to nad(p)h flux. cells with a low metabolism such as thymocytes and splenocytes reduce very little mtt. in contrast, rapidly dividing cells exhibit high rates of mtt reduction. it is important to keep in mind that assay conditions can alter metabolic activity and thus tetrazolium dye reduction without affecting cell viability. in addition, the mechanism of reduction of tetrazolium dyes, "i.e." intracellular (mtt, mts) "vs." extracellular (wst-1), will also determine the amount of product. additionally, proof has been provided as to the spontaneous mtt reduction in lipidic cellular compartments/structures, without enzymatic catalysis involved. nevertheless, even under this alternative paradigm, mtt assay still assesses the reduction potential of a cell (i.e. availability of reducing compounds to drive cellular energetics). as such, the final cell viability interpretation remains unchanged.
mtt assay
in situations lacking oxygen (a.k.a., anoxia), many cryptobionts (such as "m. tardigradum") take in water and become turgid and immobile, but can still survive for prolonged periods of time just as with other cryptobiological processes. while survival rate studies of organisms during supposed anoxybiosis in anoxia have historically given some conflicting results, the current consensus is that certain ectothermic vertebrates and some invertebrates (for example, brine shrimp (clegg et al. 1999), copepods (marcus et al., 1994), nematodes (crowe and cooper, 1971), and sponge gemmules (reiswig and miller, 1998)) are capable of successfully surviving in a seemingly inactive state during anoxic conditions for periods of time ranging from months to decades. studies of the metabolic activity of these idling organisms during anoxia have been mostly inconclusive, primarily due to the technical difficulty of measuring very small degrees of metabolic activity with enough reliability to conclusively prove a cryptobiotic state is occurring rather than just an extreme case of the metabolic rate depression (mrd) phenomenon exhibited by all aerobic organisms to some degree (typically 1-10% of aerobic levels) when exposed to anoxia. thus, anoxybiosis is not considered a legitimate form of naturally occurring cryptobiosis by some comparative biologists because of these inconclusive and conflicting experimental results regarding whether a truly complete metabolic standstill actually occurs in cryptobionts during anoxic conditions, or if the metabolism is merely such a tiny fraction of the aerobic metabolic rate that it falls below the limits of detection. also, many experts are skeptical of the biological feasibility of anoxybiosis, because any preservation of biological structures during anoxic conditions would imply that a seemingly impossible situation is occurring, wherein the organism is managing to prevent damage to its cellular structures from the environmental negative free energy despite being both surrounded by plenty of water and thermal energy and, most remarkably, it does so without using any free energy of its own. however ,as summarized by james s. clegg of the uc davis bodega marine laboratory in a 2001 review article, while many studies have failed to find measurable quantities of metabolic activity in potential anoxybiotic organisms, and there is also some evidence that the stress-induced protein p26 may act as a protein chaperone that requires no energy in cystic "artemia franciscana" embryos, more recent data suggest that most likely an extremely specialized and slow guanine polynucleotide pathway continues to provide metabolic free energy to the "artemia franciscana" embryos during anoxic conditions. although it is inherently difficult to prove that not a single organism in existence anywhere is capable of entering a truly anoxybiotic state, it seems to clearly be the case that most likely at least "a. franciscana" (a.k.a. sea monkeys, a well-known and commonly studied cryptobiont) is only capable of approaching, but not reaching, the above-mentioned implied violation of the usual biological conversion of environmental negative free energy into the negative entropy of cellular structures via metabolic processes.
cryptobiosis