Metabolic processes in cytoplasmic particles of the avocado fruit. VII. Oxidative and phosphorylative activities throughout the climacteric cycle.

Suwnmary. Mitochondria isolated from preclimacteric avocado frtuit oxidize pyrulvate at a mulch lower rate than those separated from climacteric fruit. The external addition cf thiamiine pyrophosphate (TPP) increased the rate of pyruivate oxidiation in both cases.The sttudy of the infltuence of TPP on the rate of oxidation of malate by mitochondria obtained from both preclimacteric and climacteric fruiit indicated that the effect of this cofactor coulld be uinderstood by assulming that malate was converted to pyruivate. TPP (11,12,15,24). The opportunity opened uip of followilg the variations in the oxi(lative abilities of the mitochonldria (lurinlg the overall ripening process. In the course of this stuylv it was found that the ratc of oxidation of malate was highly depencdent on the stage of the climacteric of the fruiit from which the mitochondria had been extracted. Moreover, the addition of thiamine pyrophosphate (TPP) to preclimacteric fruit particles in the presence of malate resulted in a considerable enhancement of the rate of oxidation of this substrate. At this stage of maturation the metabolism of a-ketoglutarate was also highly sensitive to the external addition of TPP (15), a situation which was not observed when the mitochondria were prepared from fruits reaching the climacteric condition,

mentioning

confidence: 99%

“…TPP (11,12,15,24). The opportunity opened uip of followilg the variations in the oxi(lative abilities of the mitochonldria (lurinlg the overall ripening process.…”

mentioning

confidence: 99%

Metabolic Processes in Cytoplasmic Particles of the Avocado Fruit. IX. The Oxidation of Pyruvate and Malate during the Climacteric Cycle

Lance¹,

Hobson²,

Young³

et al. 1967

“…The technique used throughout this study was that described by Lance et al (9) with modifications suggested by Romani and Ozelkok (22) and by Laties and Treffry (10). Each fruit was peeled, the embryo and seed coat removed, and the fruit cut into about 10 12-g pieces.…”

Section: Methodsmentioning

confidence: 99%

“…A number of proposed mechanisms have been reviewed (21). Mitochondria have been examined from several fruit including avocado (9), apple (5), and tomato (3), at various stages of the climacteric, and shown to: (a) oxidize tricarboxylic acid cycle acids at all stages; (b) exhibit respiratory control; and (c) phosphorylate efficiently at all stages of ripening. Electron micrographs show no change in the organelle morphology between preclimacteric and postclimacteric stages of avocado fruit (W. Vanderwoude and R. E. Young, personal communication).…”

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confidence: 99%

Succinoxidase Activity of Avocado Fruit Mitochondria in Relation to Temperature and Chilling Injury throughout the Climacteric Cycle

Kosiyachinda¹,

Young²

1977

Mitochondrina were isolated from 'Fuerte' avocado fruit (Persea americana Mill.) at four different stages of the respiratory climacteric. PrecUmacteric fruit had the highest rate of succinate oxidation and the postdimacteric mitochondria the lowest. Subsequently, successive additions of ADP increased the respiratory control ratio.Arrhenius plots of succinate oxidation of intact mitochondra from dimacteric rise and climacteric peak fruit showed two transition temperatures, while only one was observed in predlimacteric fruit. The low tempertore phase transition was at about 9 C, while the high one was at 20 C. In postclimacteric fruit, the low temperature transition decreased to between 5 and 2 C. The state 3 rate of succinate oxidation was highest for mitochondria from preclimacteric fruit and decreased for each later stage. The state 4 rates for preclimacteric and climacteric rise were the same, while both the climacteric peak and postclmacteric rates were about 40% lower than the predimacteric 02 uptake.The results indicate continuous changes in the mitochondrial membrane of the electron transport chain throughout the climacteric cycle.The change in the membrane influencing the phosphorylation system is greatest between cimacteric rise and peak stages. Mitochondrial membranes of postdmacteric fruit are presumed to change from flexible disordered to solid ordered phase at a lower temperature than those of other climacteric stages.The changes occurring in ripening which govern the initiation of the respiratory climacteric have not been identified. A number of proposed mechanisms have been reviewed (21). Mitochondria have been examined from several fruit including avocado (9), apple (5), and tomato (3) reflect a change in the lipid fraction of the mitochondrial membrane from a fluid to a solid phase. The change of lipid in the membrane from liquid to solid increases the activation energy of the enzyme complex by causing a conformational alteration of the membrane-bound enzyme.The change in chilling sensitivity suggested to us that ripening may be regulated by membrane lipids rather than by changes in the enzyme proteins themselves. We report here studies of Arrhenius plots of succinoxidase activity for avocado mitochondria at four stages of the respiratory climacteric as evidence for changes in the lipid components of the mitochondrial membrane. MATERIALS AND METHODSMature 'Fuerte' avocado fruit (Persea americana Mill.) of uniform size were harvested from one tree at the South Coast Field Station of the University of California at Irvine. Fruit were placed in individual 2-liter wide mouth jars at 20 C. CO2 production was monitored by Beckman model 215 IR gas analyzer as described previously (7).As soon as a fruit achieved a respiratory rate of a particular stage on the climacteric, the fruit was cooled to 2 to 4 C prior to cutting and grating. Mitochondria were isolated and immediately assayed for succinoxidase activity as described below.Isolation Procedure. The technique used throughout this study was th...

“…About 10 times more phosphate was incorporated inlto the tissue slices of cl.macteric peak fruit. Of the amounit incorporated, 1.4 % was esterified in preclimacteric slices while nearly 8 cation. Clearly, not only does phosphate enter the climacteric ,peak tissue more readily; it is also esterified more readily.…”

mentioning

confidence: 99%

Phosphorylation in Avocado Fruit Slices in Relation to the Respiratory Climacteric

Young¹,

Biale²

1967

Sumiiiary. The rate of uptake of inorganic phosphate by tissue discs from both preclimacteric and climacteric peak avocados is linear for at least 60 minutes. The loss cf 32p upon excessive washing was much greater from peak than from preclimacteric tissue. Short inctubation periods and, most important, rapid washing procedures are essential for meaningful comparisons.Phosphate esterification proceed,ed at a much greater rate in climacteric than in preclimacteric tissue. The phosphorylation was sensitive to 2,4-dinitrophenol (DNP). The A-DP to ATP ratio decreased materially with the advance of ripening. It was concluded that neither uncoupling nor acceptor control can account for the onset of the respiratory rise. Changes in permeability appear to play an important role in fruit metabol,ism during the climacteric.Many fruit exhibit a marked increase in respiratory activity shortly after picking which has been referred to as the climacteric rise in respiration. A number of explanations of this phenomenon which have been proposed but not fully sutbstantiated, have been reviewed by Biale (2), Varner (16), Spencer (15) and by Rowan (12). Millerd et al. (9) advanced the idea that at the induction of the climacteric an endogenous un-coupler of oxidative phosphorylation was formed which released a restraint on oxygen utilization. Pearson and Robertson (10) and Hulme (7) proposed a different mechanism which could also account for the rise in resipiration. They suggested that oxidation was limited by the amount of ADP available to the phosphorylative sites in the preclimacteric tissue. With the induction of the clifmacteric increased protein synthesis would tendi to increase the ADP/ATP ratio and release respiration from the restraint imposed by limiting levels of ADP.The uncoupl,ing hypothesis was supported by experiments with tissue slices which showed the addition of the uncoupler 2,4-dinitrophenol i(DNP) caused an increase in oxygen uptake in tissue slices of preclimacteric but not of clinacteric fruit (9). On the other hand, experiments with isolated mitochondria could not be explained by thiis hypothesis. Romani and Biale (11)