SEDIMENTATION OF CHEMICALLY REACTING NONDIFFUSING MACROMOLECULES. I. THEORY.
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Polyadenylated mRNA was isolated from aged slices of sweet potato root tissue and translated in a wheat germ cell-free system. The synthesis of apoprotein of the flavoprotein subunit of succinate dehydrogenase and two of the subunits of mitochondrial adenosine triphosphatase were detected by indirect immunoprecipitation. The molecular weights of the immunologically identified products were 3,000 and 8,000-9,000 daltons larger than the mature flavoprotein subunit of succinate dehydrogenase and the mature subunits of adenosine triphosphatase, respectively.
New antibodies reactive with a 20 KDal ribosomal protein of the large subunit were found in sera from two of eighty patients with systemic lupus erythematosus. This antigenic protein was identified as L12 by the mobility in two-dimensional gel electrophoresis. Both sera also contained anti-P activity against three acidic phosphoproteins (P proteins), but this activity was completely inhibited by preincubation with the isolated P proteins. Therefore, these anti-L12 can be useful for studying the function of L12 in protein synthesis.
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Cytochrome P-450LM2 was isolated from rabbit liver microsomes in a form which was shown to be homogeneous in AcA-22 Ultrogel and ultracentrifugation studies. The molecular mass determined by sedimentation equilibrium roughly corresponded to hexamer composed of 56 kDa monomers. Hexamer structure of the cytochrome was directly demonstrated by electron microscopic study. In the cytochrome P-450LM2 hexamer, monomers seem to be arranged in two layers (three monomers in the layer) in such a way that each monomer occupies a position at the vertices of a triangular antiprism with a 32 point group symmetry.
Single molecules of glycogen phosphorylase b exhibit images in the electron microscope which are similar in shape and dimension to those derived from X-ray crystallography. Phosphorylase alpha exhibits tetramers but shows dimers in the presence of glucose. Glycogen debranching enzyme appears as a monomer with an unusual crescent or shrimp-like shape, with occasional isologous aggregation to circular dimers. The longest dimension of the monomer is very similar to that of the phosphorylase dimer, 11.5 nm. Strong binding of the debranching enzyme to glycogen is readily visualized in the electron microscope. It is suggested that the distinctive shape of the debranching enzyme may be related to its catalytic function.
In rats the PAM specific activity in hypothalamic and neurohypophyseal extracts was 0.58 +/- 0.8, respectively 1.78 +/- 0.6 nmol.mg prot.-1 x h-1 (n = 5). PHM specific activity in the soluble part of the granules was higher in the neurohypophyseal than in the hypothalamic granules, and the fraction of total PHM and PAL present in the soluble part increased with the distance from the hypothalamus from some 45% to approx. 85%. Western blots of membrane and soluble granule fractions showed prevalence of higher mol. wt. forms in hypothalamic granules. It would appear that higher mol. wt. forms of PAM are processed by proteolytic enzymes during transport in the neuron and that non-neural cells in the neurohypophysis have a considerable PAM activity.
Methods for the enzyme labelling of C1q are described. The C1q conjugates have been incorporated into suitably modified C1q deviation and C1q binding assays for circulating immune complexes. These assays show the expected high positivity rate in sera from patients with systemic lupus erythematosus. The assays using enzyme labelled C1q confer considerable advantages over their counterparts using 125I.