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J B Hanson

Publications and source records attributed to J B Hanson.

At least 73 records · Page 4Linked to original sources
PubMed1968

Uncoupling of respiration-linked contraction in corn mitochondria.

Respiration-linked contraction of corn mitochondria is not noticeably reduced by low, uncoupling concentrations of dinitrophenol. However, if a contraction/respiration ratio is calculated, the contraction proves to be uncoupled. Previous statements that contraction cannot be uncoupled from respiration are in error.The uncoupling of contraction is consistent with the concept that dinitrophenol attacks a primary non-phosphorylated high energy intermediate (I approximately X). It is proposed that this intermediate is linked to some contractile mechanism such that the degree of contraction reflects the level of intermediate.

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PubMed1967

Uncoupling of energy-linked functions of corn mitochondria by linoleic Acid and monomethyldecenylsuccinic Acid.

Linoleic acid and monomethyldecenylsuccinic acid were tested as uncoupling agents for energy linked functions of corn mitochondria. 2,4-dinitrophenol was used as a standard for comparison. Both compounds uncoupled oxidative phosphorylation, released oligomycin-blocked respiration, and accelerated adenosine triphosphatase. Linoleic acid uncoupled calcium-activated phosphate accumulation and the increase in light scattering that accompanies the accumulation. Unlike dinitrophenol, linoleic acid at 0.1 mm had a destructive effect on membrane semipermeability. Kinetic studies indicated that dinitrophenol and linoleic acid compete with phosphate for active sites in oxidative phosphorylation.Some linoleic acid is taken up by respiring mitochondria and a major share of the uptake is incorporated into phospholipids. Calcium ion and oligomycin promote the uptake, but coenzyme A does not. It is deduced that fatty acid probably attacks the non-phosphorylated intermediate, I approximately X, producing X approximately acyl. Uncoupling results from breakdown of X approximately acyl, but sufficient X approximately acyl is maintained to serve as a source of activated fatty acid.

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PubMed1966

Contracted state as an energy source for ca binding and ca + inorganic phosphate accumulation by corn mitochondria.

An investigation has been made of the possibility of utilizing the potential energy of the contracted state of corn mitochondria to drive Ca + inorganic phosphate accumulation. Contraction was obtained with succinate or NADH oxidation. In the succinate experiments the mitochondria were contracted in buffered KCl layered over sucrose in centrifuge tubes and centrifuged down through distinct wash, reactive and isotope exchange layers. In the NADH experiments, ion accumulation was initiated upon exhaustion of the substrate. The results show that mitochondria in the contracted state will actively bind some (45)Ca, but no real accumulation occurs until inorganic phosphate is available. Substrate powered contraction in the presence of inorganic phosphate also provides a potential for accumulation upon subsequent reaction of the mitochondria with Ca. It is deducted that contraction is due to X approximately I formation, to which Ca will bind. Subsequent reaction with inorganic phosphate produces CaX approximately P, which is the transport moiety. When X approximately P is formed first, Ca also reacts to produce CaX approximately P. Hence it is immaterial which ion reacts first with the contracted state. Contraction is believed to result from the action of a mechanoenzyme, presumably I approximately . The stability of CaX approximately I must be low for the mitochondria swell very rapidly upon exhaustion of NADH or blocking of succinate oxidation by cyanide.

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PubMed1966

Swelling and contraction of corn mitochondria.

A survey has been made of the properties of corn mitochondria in swelling and contraction. The mitochondria swell spontaneously in KCl but not in sucrose. Aged mitochondria will swell rapidly in sucrose if treated with citrate or EDTA. Swelling does not impair oxidative phosphorylation if bovine serum albumin is present.Contraction can be maintained or initiated with ATP + Mg or an oxidizable substrate, contraction being more rapid with the substrate. Magnesium is not required for substrate powered contraction. Contraction powered by ATP is accompanied by the release of phosphate. Oligomycin inhibits both ATP-powered contraction and the release of phosphate. However, it does not affect substrate-powered contraction. Substrate powered contraction is inhibited by electron-transport inhibitors. The uncoupler, carbonyl cyanide m-chlorophenyl hydrazone, accelerates swelling and inhibits both ATP-and substrate-powered contraction. However, the concentrations required are well in excess of those required to produce uncoupling and to accelerate adenosine triphosphatase; the concentrations required inhibit respiration in a phosphorylating medium.Phosphate is a very effective inhibitor of succinate-powered contraction. Neither oligomycin nor Mg affects the phosphate inhibition. Phosphate is less inhibitory with the ATP-powered contraction.The results are discussed in terms of a hypothesis that contraction is associated with a nonphosphorylated high energy intermediate of oxidative phosphorylation.

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PubMed1966

Calcium-activated phosphate uptake in contracting corn mitochondria.

The phosphate inhibition of succinate-powered contraction in corn mitochondria can be reversed with calcium. Associated with this reversal is an accumulation of phosphate and calcium. Both ions are essential for accumulation, although strontium will partially substitute for calcium. Arsenate does not substitute for phosphate except in producing the inhibition of contraction.The antibiotics oligomycin and aurovertin do not block the phosphate inhibition of contraction or the calcium-activated phosphate uptake associated with the release of the inhibition. Dinitrophenol uncouples the phosphate uptake but permits full contraction.Calcium promotes inorganic phosphate accumulation in root tissue as well as in mitochondria.The results are discussed from the viewpoint of theories of calcium reaction with high energy intermediates of oxidative phosphorylation. It is concluded that calcium probably reacts with X approximately P in corn mitochondria, rather than with X approximately I as with animal mitochondria.

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