Preparation and properties of a mitochondrial fraction from carrot tissue

The effect of protein concentration on the activity of beta-fructosidase from radish seedlings

Radish beta-fructosidase (beta-D-fructofuranoside fructohydrolase, EC 3.2.1.26) is inactived by diluting the enzyme solution and the activity can be restored by addition of bovine serum albumin or other proteins. The use of detergent, high molar salt solutions or silicone-coated tubes showed that decrease of specific activity upon dilution is not linked to adsorption of the enzyme on to glass walls. Albumin neither protects the enzyme from denaturation by heat nor changes its stability during conservation at room temperature. The action of added proteins is not due to removal of an inhibitor from the enzyme solutions. Some polyanions or polycations have the same effect as albumin, but dialysis or chromatography show that they do not act by reassociation of inactive products formed by dilution of the active enzyme. A molecular weight heterogeneity is observed in the enzyme population when chromatography is performed without albumin. This suggests that inactive forms, formed upon dilution, differ slightly in their molecular conformation from the active forms obtained at high protein concentration.

Necessary conditions for isolation of tightly coupled higher plant mitochondria

A number of parameters associated with the isolation of plant mitochondria were carefully examined in the hope of optimizing the isolation technique. Dark-grown mung bean (Phaseolus aureus var. Jumbo) hypocotyls were used as the source of mitochondria. Necessary conditions for the isolation of tightly coupled plant mitochondria include: (a) gentle tissue disruption; (b) rigorous exclusion of contaminating particles from the mitochondrial fraction; (c) the use of an optimal grinding medium containing a high concentration of mannitol, 10 mm phosphate or triethanolamine buffer to maintain the pH above 7.2, ethylenediaminetetraacetic acid at 1 mm level, cysteine at a low concentration (0-5 mm), and a high concentration of bovine serum albumin (0.1-1.0%); and (d) the use of the proper wash and suspending medium consisting of mannitol, buffer, and bovine serum albumin at the same concentration as in the grinding medium.

PREPARATION AND PROPERTIES OF A MITOCHONDRIAL FRACTION FROM WHEAT STEM RUST UREDOSPORES

Ungerminated uredospores of Puccinia graminis f. sp. tritici Erikss. & Henn. race 15B were disrupted in a buffered sucrose serum albumin solution, using a "Teflon" pestle homogenizer and glass beads 80 μ in diameter. A particulate fraction was sedimented between 2000 and 30,000 × g and its oxidation of Krebs' cycle acids measured manometrically. Endogenous respiration of washed preparations was low or negligible. Oxygen uptake was observed with succinate (40 to 60 μl/hour mg protein), α-ketoglutarate, malate, citrate, and isocitrate (10 to 30 μl/hour mg protein) but not with fumarate or pyruvate. Succinate oxidation was sensitive to heat, cyanide, and malonate.Aspects of the extraction procedure were examined for effects on yield and activity. Serum albumin in the grinding medium, very low grinding speed, and short grinding time favored high activity per mg protein. Glass beads increased the yield with the "Teflon" pestle while an all-glass homogenizer gave preparations of low activity.Oxidatively active particle suspensions reduced Janus green B and were shown by electron microscopy to consist of vesicles and some mitochondria.