Three functionally different cytochrome b redox centres in pigeon heart mitochondria

Skeletal muscle bioenergetics: a comparative study of mitochondria isolated from pigeon pectoralis, rat soleus, rat biceps brachii, pig biceps femoris and human quadriceps

The metabolism of mitochondria isolated from five functionally different skeletal muscles is compared. Data for a single ectothermic preparation are also reported. The mitochondria were prepared in yields of 44+/-7% from 50 to 100 mg muscle. The muscle content of mitochondrial protein ranged between 2 and 40 g kg(-1). Twelve specific activities of key enzymes and metabolic systems were determined, 10 of these in functional assays with respiratory measurements. The specific activities of glutamate dehydrogenase, alpha-glycerophosphate dehydrogenase, and exo-NADH oxidase differed considerably among muscle sources. Seven specific activities, including very central reactions, showed low among-muscle variation. The activity of ATP synthesis, for instance, was 1.0-1.3 mmol min(-1) g(-1) mitochondrial protein, 25 degrees C. In vitro data were extrapolated to in vivo conditions of the muscles. The calculated rates of respiration and ATP synthesis were in accordance with reported tissue activities. Pigeon pectoralis mitochondria showed a unique cytochrome spectrum and a respiratory chain activity that might effect simultaneous carbohydrate and fatty acid respiration. In mitochondria from the other muscles, the respiratory chain activity balanced the carbohydrate oxidation capacity. In all muscles, the respiratory capacity exceeds that needed for oxidative phosphorylation. This may secure maximal mitochondrial ATP synthesis during maximal work rates and high cellular [Ca(2+)].

Experimental evidence against the mitochondrial theory of aging. A study of isolated human skeletal muscle mitochondria

The mitochondrial theory of aging was tested with optimised preparation techniques. Mitochondria were isolated from approximately 90 mg quadriceps muscle from healthy humans at age 70+ and 20+. The content of mitochondrial protein was approximately 10 mg g(-1) muscle and the yields were approximately 40%. The mitochondrial integrity was high as judged from the respiratory control and P/O ratios. No general membrane alterations or changes in the cytochrome contents were observed. BSA decreased the non-phosphorylating rates of respiration equally in both age groups. Thirteen different enzyme activities were assayed and normalised to protein content and citrate synthase activity. Most of the critical levels for detection of declines were <10%. In the 70+ group, the activity for fatty acid oxidation was decreased by approximately 20%. Two inherently low activities associated with oxidation of sarcoplasmic NADH were also decreased, probably related to the age change of fibre types. The remaining activities measured, e.g. those of pyruvate dehydrogenase, tricarboxylic acid cycle, respiratory chain, and ATP synthesis, were not observed to be lowered. Thus, the central bioenergetic systems appeared unaltered with age. The obvious discord with reported age declines of human skeletal muscle mitochondrial function is discussed. It is concluded that the present results are incompatible with the mitochondrial theory of aging.

Optimization of preparation of mitochondria from 25-100 mg skeletal muscle

A method for isolation of mitochondria from 25-100 mg skeletal muscle is described. The instrumental developments include a refined homogenization setup, special handling techniques, and equipment for biopsy storage. The preparation medium was a standard ionic medium. All fractions were assayed for marker enzymes and the data used in optimization of the yield. It was observed that the homogenization procedure exerts strong control on the integrity of the isolated mitochondria. The method was developed with pigeon breast muscle as the model tissue and used virtually unaltered for preparation from muscles of pigs, rats, and humans. The relative yield was 40-50% and the mitochondria were well coupled and showed high rates of phosphorylating respiration.

Small scale preparation of skeletal muscle mitochondria, criteria of integrity, and assays with reference to tissue function

Mitochondria prepared in small scale from skeletal muscle were studied with respiration measurements and low temperature spectroscopy. The method of preparation was developed for 25-100 mg tissue with pigeon breast muscle as model organ. The yield was 40%. Data collected during the developmental work were used to evaluate criteria of mitochondrial quality. The cytochrome c conservation, i.e. cytochrome c per mitochondrial quantity in the preparation relative to that in the tissue, is a most useful test parameter. It is bounded between 0-100%. Proportionality between the state 3 rate and the cytochrome c conservation was not rejected by statistical tests. The respiratory control ratio (RCR) was also highly correlated to the cytochrome c conservation. These correlations might be extrapolated to 100% conservation to give hypothetical tissue values. The cause for the correlations is discussed. The P/O ratio showed only weak dependence on the cytochrome c conservation and the state 4 rate showed no dependence. Other, rather insensitive test parameters are also discussed. The pigeon breast muscle mitochondria isolated by the final method showed cytochrome c conservation of 73 +/- 9% (n = 16). They are compared with pig biceps femoris mitochondria prepared by the same method. The two types of mitochondria show many similarities. Some differences may be explained by a different amount of inner mitochondrial membrane relative to mitochondrial protein. The pig tissue contains ten times less mitochondrial protein than the pigeon tissue does.

Characterization of mitochondria from pig muscle: higher activity of exo-NADH oxidase in animals suffering from malignant hyperthermia

Mitochondria were isolated from biopsies of the biceps femoris muscle of Danish landrace pigs. Three groups of animals were compared: (1) normal pigs; (2) pigs that were homozygous with respect to the gene Hal(n)/Hal(n) coding for the porcine malignant hyperthermia syndrome; and (3) heterozygote animals. A newly developed micro-method for preparation and assaying of small quantities of intact mitochondria was employed. With this technique mitochondria from biopsies weighing less than 100 mg were examined with respect to cytochrome content as well as phosphorylating and respiratory activities, including the nonphosphorylating exo-NADH oxidase activity. The mitochondria, prepared in a yield of 48%, showed high respiratory activities with tricarboxylic acid-cycle intermediates and pyruvate, and somewhat lower activity with palmitoyl-carnitine as substrate. The ATP synthase activity was about 1000 micromol ATP/min per g of protein and the maximal respiratory activity approx. 700 micromol of O2/min per g of protein. No differences among the three groups of animals were detected, except for the exo-NADH oxidase activities, which were 43, 78 and 107 micromol of O2/min per g of protein in the groups of normal, heterozygous and homozygous animals respectively. It is concluded that the exo-NADH oxidase activity may be a genetic manifestation of malignant hyperthermia and may play a significant role in the heat production characteristic of the syndrome.

Isolation of chromaffin cell thapsigargin-sensitive Ca2+ store in light microsomes from bovine adrenal medulla

1. A subcellular fractionation procedure for bovine adrenal glands was designed with the aim to study the biochemical properties of Ca2+ stores in chromaffin cells. 2. The thapsigargin-sensitive compartment of Ca2+ stores was found to be highly enriched in a light microsomal fraction (LMF) on a 15-30% linear sucrose gradient, and was found to be essentially devoid of contamination by plasma, mitochondrial or secretory granule membranes. 3. A Ca(2+)-pumping ATPase was identified in this LMF as a 97 kDa protein forming an acid-stable, Ca(2+)-dependent, thapsigargin-sensitive phosphorylated intermediate upon incubation with [gamma-32P]ATP, suggesting this protein to represent a SERCA-3 isoform of Ca2+ ATPases. 4. A major 162 kDa protein, previously demonstrated in the isolated chromaffin cells, was enriched in the LMF, distributing on sucrose gradients in parallel with the thapsigargin-sensitive Ca2+ uptake. 5. LMF appears to represent a part of the thapsigargin-sensitive Ca2+ store of chromaffin cells, and should be useful for further studies of the store properties at the subcellular and molecular level.

Ubiquinone reduction pattern in pigeon heart mitochondria. Identification of three distinct ubiquinone pools

Intact pigeon heart mitochondria showed 10-30% ubiquinone reduction in the absence of substrates. This reduction could not be ascribed to endogenous substrates, as judged by lack of effect of inhibitors and uncouplers and by the very low endogenous respiratory rate. Addition of NADH in the presence of antimycin caused further reduction of about 10% ubiquinone, apparently coupled to the rotenone- and antimycin-sensitive exo-NADH oxidase system [Rasmussen (1969) FEBS Lett. 2, 157-162]. Citric acid cycle substrates reduced most of the remaining ubiquinone in the presence of antimycin; 15-20% of the total ubiquinone content was still in the oxidized form under the most reducing conditions. Three pools of ubiquinone therefore appeared to be present in heart mitochondria: a metabolically inactive pool consisting of reduced as well as oxidized ubiquinone, a pool coupled to oxidation of added (cytoplasmic) NADH, and the well-known pool coupled to citric acid cycle oxidations. Ferricyanide selectively oxidized the ubiquinol reduced by added NADH, indicating that this pool is situated on the outer surface of the mitochondrial inner membrane. Ubiquinone reduction levels were determined with a new method, which is described in detail.

The NADH oxidase system (external) of muscle mitochondria and its role in the oxidation of cytoplasmic NADH

An exo-NADH oxidase system [NADH oxidase system (external)], effecting intact-mitochondrial oxidation of added NADH, was studied in pigeon heart mitochondria. Breast muscle mitochondria showed an equal specific activity of the system. The exo-NADH oxidase activity (200 micron mol of NADH/min per g of protein) equalled two-thirds of the State-3 respiratory activity with malate + pyruvate or one-seventh of the total NADH oxidase activity of heart mitochondria. The activity was not caused by use of proteinase in the preparation procedure and all measured parameters were very reproducible from preparation to preparation. The activity is therefore most likely not due to preparation artefacts. The exo-NADH oxidase system is present in all mitochondria in the preparation and is not confined to a subpopulation. The system reduced all cytochrome anaerobically and direct interaction with all cytochrome oxidase was demonstrated by interdependent cyanide inhibition. The exo-NADH oxidase system seems to be located at the outer surface of the mitochondrial inner membrane because, for instance, only this system was rapidly inhibited by rotenone, and ferricyanide could act as acceptor in the rotenone-inhibited system (reductase activity = 20 times oxidase activity). In the presence of antimycin, added NADH reduced only a part of the b-cytochromes. Freezing and thawing the mitochondria, one of the methods used for making them permeable to NADH, destroyed this functional compartmentation. The characteristics of the exo-NADH oxidase system and the malate-aspartate shuttle are compared and the evidence for the shuttle's function in heart in vivo is re-evaluated. It is proposed that oxidation of cytoplasmic NADH in red muscles primarily is effected by the exo-NADH oxidase system.