On the structure of liver ribosomes

The morphology of liver ribosomes and their subparticles, large and small, has been investigated. Analysis of the images has been carried out by successive selection of models and by X-raying them under conditions simulating negative staining. The relation between the main views has been checked by tilting the specimens in an electron microscope through ± 30 °.The small subparticle consists of an elongated body, to one of the ends of which a short “head” is attached. A model has been proposed, whose projections on rotation with respect to the longitudinal axis would satisfy all observable types of images. According to the proposed model, the “head” is tilted with respect to the elongated portion. The length of the subparticle is 230 Å. The dimensions of the elongated portion in the transverse direction are 110 Å × 75 to 80 Å.The large subparticles in lateral view resemble short “rods” 220 to 240 Å long and about 70 to 95 Å wide. At a distance of about 60 Å from the left end of the particles a projection (60 Å in length) is seen, on the inner side of which a depression, or “channel”, filled with the contrasting substance is always observed. Next to this depression a second projection is located, whose height is about 30 Å. The channel is either a cavity in the body of the large subparticle or a part of the RNA without protein. The length of the channel is about 80 Å, the width is about 50 to 60 Å. The left end of the particles is characterized by two sharpened portions; as a result, a cavity that shows an obtuse angle profile makes its appearance. The opposite end of the particles is cut off at an angle of 45 °. In another view, the subparticles appear to be almost rectangular in shape; they are characterized by dimensions of 150 Å × 220 to 240 Å. It is likely that the large projection is displaced sideways with respect to the longitudinal axis of the particles. The asymmetry associated with this displacement gives rise to preferred arrangements of the subparticles on the supporting film. An analysis has been made of the most typical images of monomeric ribosomes, on the basis of which a suggestion is made about mutual orientation of subparticles in a monomer.     

On the metabolic function of heparin-releasable liver lipase

Intravenous administration of specific antibody against heparin-releasable liver lipase (liver lipase) induced a 75% inhibition of the enzyme activity $\text{in situ}$. Administration of the antibody resulted in an increase of high density lipoprotein (density range 1.050–1.13 g/ml; HDL₂) phospholipid levels (20% after 1 h; 54% after 4 h). Short-term (1 h) treatment with antibody had no significant effect on any of the other lipoprotein components. After long-term (4 h) treatment the free cholesterol level of HDL₂ and all components in the very low density lipoprotein (VLDL) + intermediate density lipoprotein (IDL) fraction were elevated (1.5–2.0 fold). In the low density lipoprotein (LDL) fraction only the phospholipid level was affected (increased by 72%). All lipid components in the HDL₃ fraction were decreased by the antibody treatment, but this decrease was only statistically significant for the cholesterolesters. The rate of removal of iodine-labeled high density lipoprotein (HDL) and LDL from serum was not affected by the antibody treatment.These results suggest that liver lipase may promote phospholipid removal $\text{in vivo}$ and show that a lowering of liver lipase $\text{in situ}$ has profound consequences for serum lipoprotein metabolism.     

On the intrinsic innervation of normal rat liver

Summary With the Bodian method stained fibers were observed in the lobules of the rat liver and with the modified Karnovsky and Roots thiocholine method cholinesterase (presumably acetylcholinesterase (AChE))-positive nerve fibers were found in a pattern similar to that of the Bodian-stained fibers. The AChE positive nerve fibers form a network in the liver lobules in close relation to hepatocytes and sinusoids. Fluorescent varicose nerve fibers demonstrated by the glyoxylic acid and Falck-Hillarp fluorescence methods were found only in the interlobular spaces associated with vessels. As no overlapping of distribution patterns of AChE-positive nerve fibers and fluorescent nerve fibers occurs, the AChE activity of the nerves of the liver lobules probably reflects the associated presence of acetylcholine in the nerve fibers. In consequence we suggest that nerves of the liver lobules belong to the autonomic parasympathetic nervous system.SEM of liver tissue revealed light cords apparently situated in smooth surfaced channels between adjacent hepatocytes and in the space of Disse, where fibers also cross sinusoids. We tentatively suggest that the cords of the SEM represent the AChE-positive nerve fibers of our LM observations'.The skilled assistance of Dr. Esther Hage, Department of Pathology, Odense Sygehus, Denmark, in the Falck-Hillarp fluorescence work is gratefully acknowledged     

On the multiplicity of rat liver glutathione S-transferases

Rat liver glutathione S-transferases have been purified to apparent electrophoretic homogeneity by S-hexylglutathione-linked Sepharose 6B affinity chromatography and CM-cellulose column chromatography. At least 11 transferase activity peaks can be resolved including five Yb size homodimeric isozymes, two Yc size homodimeric isozymes, one Ya homodimeric isozyme, one Y alpha homodimeric isozyme, and two Ya-Yc heterodimeric isozymes. Distribution of the GSH peroxidase activity among the CM-cellulose column fractions suggests the existence of further multiplicity in this isozyme family. Substrate specificity patterns of the Yb subunit isozymes revealed a possibility that each of the five Yb-containing isozymes is composed of a different homodimeric Yb size subunit composition. Our findings on the increasing multiplicity of glutathione S-transferase isozymes are consistent with the notion that multiple isozymes of overlapping substrate specificities are required to detoxify a multitude of xenobiotics in addition to serving other important physiological functions.     

On the multiplicity of the enzyme catalase in mammalian liver

Summary The literature on the complex multiplicity of mammlian catalase and the nature of the epigenetic modifications undergone by this enzyme has been reviewed, along with relevant comment on the subcellular localization and biological role of the enzyme.The epigenetic causations of multiplicity are established as being multifactorial and include oxidoreductive conversions of sulphydryl groups, the covalent attachment of carbohydrate, and partial proteolysis of the enzyme. Each of these epigenetic transformations may give rise to sets of multiple forms, and overlaps between these separate sets may give rise to extremely complex multiplicity patterns.It is concluded that any interpretation of catalase multiplicity which places emphasis on a single epigenetic causation is not compatible with the scope and variety of the available data on this enzyme. Instead, a holistic approach is urged — one giving due emphasis to the multiple causation of catalase multiplicity, and the interrelationships of these causations in the cellular situation. Rather than viewing the multiplicity of this enzyme as merely a series of interesting chemical modifications, emphasis is directed towards the fact that catalase heterogeneity povides a sensitive indication of the functional variations which occur within separate compartments of the subcellular structure, and hence becomes an essential element in any satisfactory understanding of the role of this enzyme in cellular processes.     

On the kinetics of liver enzyme regression following induction

It is shown that a number of workers have incorrectly considered that the rate of decline (regression) of induced liver enzyme activity is directly proportional to the actual enzyme concentration whereas both theory and observation indicate that the decay curve is a function of both a first-order degradation rate and a counteracting zero-order normal rate of synthesis. Thus, semilogarithmic plots of actual enzyme concentration as a function of time during regression have resulted in the appearance in the literature of spuriously high values for the half-lives of several enzymes and/or erroneously low values for their degradation rate constants. Since these constants are a major factor in the analysis of enzyme induction kinetics, the accuracy of their determination from activity regression data is extremely important. The correct method for treating such data is reiterated.     

On the mechanism of spermine transport in liver mitochondria

Spermine penetrates the mitochondrial matrix at significant rates which increase sharply and non-ohmically with membrane potential. In this respect, spermine uptake is qualitatively similar to that of other cations whose electrophoretic transport has been studied in mitochondria. At 200 mV and 1 mM spermine, the observed rate of spermine uptake was about 7 nmol x mg-1 x min-1, and the rate constant was about 8 times greater than that of tetraethylammonium cation. These rates are remarkably rapid considering that spermine is largely tetravalent at the pH of the experiment. The fluxes of spermine and tetraethylammonium are log-linear with membrane potential. The slope of the tetraethylammonium plot is consistent with leakage of this ion across a sharp Eyring barrier located in the middle of the membrane. The slope of the spermine plot is half that predicted by such a leak pathway, raising the possibility that spermine may cross the inner membrane by means of a channel. Whatever its mechanism of penetration, if comparable rates of uptake obtain in vivo and if spermine is not metabolized within the mitochondrial matrix, then a separate efflux mechanism would appear to be required to prevent unlimited spermine loading.