Biochimica et Biophysica Acta (BBA) - Enzymology and Biological Oxidation最新文献

• 1.

  1. A bound fraction of grabe $\text{β-}\text{fructofuranosidase}$ (EC 3.2.1.26) was solubilized by treatment with 0.2 M borate buffer (pH 8.5), whereas several other aqueous salts were without effect.

• 2.

  2. In the system described, solubilization was influenced by boric acid concentration and pH but not by presentation time. Solubilization was essentially irreversible.

• 3.

  3. Solubilization was maximal at pH 8.5; under more alkaline conditions, enzyme inactivation occurred. The decrease in amount of bound enzyme followed an inverse trend.

• 4.

  4. Borate solubilization gave a total yield of $\text{β-}\text{fructofuranosidase}$ about 190% based on the starting material. This, together with the well-known interaction of borate with carbohydrates, suggested that a masking polysaccharide was operative in the starting material.

• 5.

  5. The solubilized and soluble enzyme were partially purified and characterized. In both cases, only unsubstituted β-fructofuranosides were hydrolyzed. The Michaelis constants for sucrose were not significantly different.

• 6.

  6. The dangers inherent in comparing the relative amounts of enzymes from different tissues were underlined by this experience.

The chromatography of liver homogenates and purified preparations of human-liver arginase (l-arginine ureohydrolase, EC 3.5.3.1) on CM-cellulose separates two protein fractions with arginase activity. On rechromatography, each of these fractions appears homogeneous and retains its adsorption-elution characteristics.

Both arginase fractions have similar properties as far as their affinities for substrates, pH optima and thermal inactivation are concerned. However, they differ in their pH stabilities and in their inhibition by ornithine and canavanine.

• 1.

  1. The formation of NADH-X from NADH in the presence of glyceraldehyde phosphate dehydrogenase (EC 1.2.1.12) at low pH is observed not only in the presence of pyrophosphate, citrate or phosphate, but also in the presence of arsenate.

• 2.

  2. Stimulation of NADH-X formation by acetyl phosphate is dependent on the presence of enzyme-bound NAD⁺; however, added NAD⁺ is inhibitory.

• 3.

  3. Inhibition of NADH-X formation by sulphydryl reagents is prevented by acetyl phosphate in the presence of pyrophosphate or citrate, but not in the presence of arsenate or phosphate.

• 4.

  4. In the absence of other polyvalent anions, acetyl phosphate alone can stimulate the conversion of NADH into NADH-X at low pH.

• 5.

  5. In the presence of acetyl phosphate, the relative rate of formation of NAD⁺ and NADH-X from NADH is dependent on the pH and the anions present.

A procedure is described for isolating mitochondria from the thoracic muscle of the southern armyworm moth, Prodenia eridania. These mitochondria are capable of very rapidly oxidizing palmitate with concomitant phosphorylation of adenosine 5′-diphosphate. There is an absolute requirement for adenosine 5′-diphosphate and inorganic phosphate, but added nicotinamide-adenine dinucleotide, nicotinamide-adenine dinucleotide phosphate and carnitine have no effect. Maximal rates of oxygen uptake are found when a high-energy phosphate trap and some protein are present.

Morphological changes of rat-liver mitochondria brought about by swelling and ATP-induced contraction were studied by electron microscopy. The course of swelling is proposed to be as follows: Entering of water (and solutes) causes breakage of the outer membrane and formation of protrusion of the inner membrane. The distention of the inner membrane is accompanied by loss of density of the matrix and by disapperance and change of shape of the cristae, probably due to their unfolding and evagination. Both membranes seem to possess a limited ability to stretch.

Addition of ATP to mitochondria swollen in the presence of either orthophosphate, oleate and thyroxine gave rise to structures different from mitochondria before the onset of swelling. Restoration of the mitochondrial morphology was not observed. It is thought that the processes initiated by ATP are not a simple reversal of swelling.