Isolation and characterization of an apoprotein from the d less than 1.006 lipoproteins of human and canine lymph homologous with the rat A-IV apoprotein.

The singlet oxygen traps, 2,5-diphenylfurane and 1,3-diphenylisobenzofurane were oxidized to cis-benzoylethylene and o-dibenzoylbenzene during the decomposition of diisopropyl-N-nitrosamine catalyzed by peroxidase. Singlet oxygen quenchers inhibited this conversion and also the chemiluminescence accompaying the catalyzed reaction. The chemiluminescence is enhanced by 1,4-diazobicyclo (2.2.2) octane, fluorescein, eosin rhodamine B and rose bengal but little effect was detected in the presence of 9,10-dibromoanthracene-2-sulfonate, 9,10-diphenylanthracene-2-sulfonate and anthracene-2-sulfonate. An emission spectrum of the unsensitized reaction in 560 – 600 nm region was observed. It is concluded that singlet oxygen is formed during peroxidase catalyzed degradation of diisopropyl-N-nitrosamine.     

Suppression of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity and of incorporation of acetate into cholesterol in homozygous hypercholesterolemic fibroblasts by ferritin-low density lipoprotein conjugates.

Conjugates of ferritin with low density lipoproteins (LDL) were prepared and separated by sucrose gradient centrifugation. These conjugates, at cholesterol concentration of 100--132 microgram/ml, caused a greater than 90% suppression of hydroxymethylglutaryl coenzyme A reductase activity and of acetate incorporation into cholesterol in cultured skin fibroblasts from a normal subject as well as from a subject with homozygous familial hypercholesterolemia. The half maximal inhibition concentration was approx. 10 microgram/ml cholesterol for LDL and ferritin . (LDL)2 and 5 microgram/ml for (ferritin)2 . LDL in both cell lines. In contrast, native low density lipoproteins have only a minimal inhibitory effect in homozygous cells. The ability of the conjugates to stimulate the incorporation of oleate into cholesteryl esters was also equal in the two cell lines, although the conjugates were only 10% as active as low density lipoproteins in the normal cells. LDL reduced the ferritin . (LDL)2-mediated suppression of hydroxymethylglutaryl-CoA reductase activity in homozygous cells while ferritin . (LDL)2 reduced the LDL-mediated stimulation of cholesteryl ester formation in normal cells.     

Characterization of sterol-ester hydrolase in Saccharomyces cerevisiae.

A homgenate of Saccharomyces cerevisiae grown under semi-anaerobic as well as aerobic conditions was found to catalyze the hydrolysis of fatty acid esters of sterols in the presence of Triton X-100. The enzyme levels in cells grown under various conditions were similar and the enzyme had a broad substrate specificity for sterol esters. The enzyme was localized in the mitochondrial fraction for the aerobically grown cells and in the mitochondrial and cytosolic fractions for the semi-anaerobically grown cells.     

Effect of calcium on extraction of Z-band proteins from I-Z-I brushes of rabbit striated muscle.

1. When rabbit striated muscle I-Z-I brushes were subjected to eleven extractions with three different extracting solutions, relatively more amount of proteins was extracted in the presence of 1 nM CaCl2 than in the presence of 5 mM EDTA or 5 mM ethyleneglycol-bisp(beta-aminoethylether)-N,N,N1,N1-tetra-acetic acid (EGTA). Among proteins extracted in the presence of 1 mM CaCl2, the protein components with molecular weights of 85,000, 95,000 and 220,000 were included, whereas these were not extracted in the other two. 2. Co-electrophoreses of 220,000 dalton protein and myosin heavy chain showed that these two protein components were distinct from each other. 3. Roles of Ca2+ are discussed on disintegration processes of I-Z-I brushes in special reference to its co-operative action with calcium-activated factor enzyme.     

Heat-induced changes of chlorophyll fluorescence in isolated chloroplasts and related heat-damage at the pigment level

The heat-induced changes of chlorophyll fluorescence excitation and emission properties were studied in isolated chloroplasts of Larrea divaricata Cav. An analysis of the temperature dependency of fluorescence, under Fo and Fmax conditions, of temperature-jump fluorescence induction kinetics, and of 77 degrees K emission spectra of preheated chloroplasts revealed two major components in the heat-induced fluorescence changes: (1) a fluorescence rise, reflecting the block of Photosystem II reaction centers; and (2) a fluorescence decrease, caused by the functional separation of light-harvesting pigment protein complex from the rest of the pigment system. Preferential excitation of chlorophyll a around 420 nm, produced a predominant fluorescence rise. Preferential excitation of chlorophyll b, at 480 nm, gives a predominant fluorescence decrease. It is proposed that the overlapping of the fluorescence decrease on the somewhat faster fluorescence rise, results in the biphasic fluorescence rise kinetics observed in isolated chloroplasts. Both the rise component and the decay component are affected by the thermal stability of the chloroplasts, acquired during growth of the plants in different thermal environments. Mg2+ enhances the stability against heat-damage expressed in the decrease component, but has no effect on the rise component. Heat pretreatment leads to a decrease of the variable fluorescence in the light-induced 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) rise curve, but no change in half-rise time is observed. It is concluded that the block of Photosystem II reaction centers precedes the loss of the light-harvesting pigment protein complex. However, the approximately antiparallel heat-induced Fmax decrease and Fo increase suggest a common cause for the two events. A heat-induced perturbation of the thylakoid membrane is discussed.     

Dark transition of 1st level reduction products of porphyrins to 2d level

Transition of the products of the first restoration of porphyrines to the second one in the darkness and practically in the absence of a reducer and oxygen has been studied. Its cause is the disproportioning of dyhydroform into tetrahydro- and the initial pigment. Regeneration of porphyrines under these conditions is also shown. The rate of both reactions significantly increases in the light.     

Formation kinetics of the AT-specific complex: DNA-distamycin A

The kinetics of DNA-distamycin A complex formation and dissociation was studied by means of the stop-flow method. It has been found that the complex formation has at least five steps, the formation of AT-specific complex is limited by the dissociation of less specific intermediate complexes, then follows the statistical rearrangement of the ligand molecules and "fixation" of the specific complex with the longest lifetime and the biggest number of the additional H-bounds with the matrix. The energy of a single specific H-bond between the ligand molecule and AT-pair is equal to--1.05 kcal/mol.     

Study of the conformational mobility of globular proteins in aqueous solutions according to their proton relaxation in a rotating system of coordinates

Measurements of the nuclear magnetization decay in the rotating frame for protons of SA and RNAase proteins in aqueous solutions indicate the dispersion of the relaxation rate for SA protons within the region of correlation frequencies of 10(5)--10(6) s-1. These frequencies are much lower than frequencies of rotational diffusion movements of the SA macromolecules in aqueous solutions. These must be ascribed to internal movement within protein globules due to which the distances between interacting magnetic moments are changed. This conclusion gives direct evidence in favour of existence of conformational mobility in most of the protein globule volume.     

A proposed mechanism relating the antitumor behavior of cis-platinum amine complexes to their inhibition of a model enzyme

The twenty-four hour inhibition of m-malate dehydrogenase (E.C. 1.1.1.37) by various complexes of cis-platinum(II) and cis-platinum(IV) was measured as a function of the platinum concentration. It was observed that increased alkylation of the amine groups of Pt(II) and to a lesser degree of Pt(IV) decreased the activity consistently. It was also observed that the Pt(IV) analogues inhibit the enzyme to about an order of magnitude greater than the Pt(II) complexes. These phenomena will be interpreted.