Ribosomes in growing and non-growing bacterial cells

1. 1.
   It was found that growing cells always contained more different groups of ribosomes and their total amount was greater than in non-growing cells or spores, in which only two ribosome groups with different sedimentation constants, according to the species of microorganism, were consistently found.     
   
   

Thymidine kinase and deoxyribonucleic acid metabolism in growing and regenerating livers from rats on controlled feeding schedules

Rats accustomed to eating during the first 8h of a daily 12h dark period re-established about 80% of intact liver weight, protein and DNA within 4 days following partial hepatectomy; further increases were not observed. Liver thymidine kinase activity and thymidine incorporation into liver DNA exhibited marked daily oscillations during liver regeneration. Maximum values were observed near the end of the dark period both in intact growing rats and in rats partially hepatectomized 2h before the end of the dark period. The time of day of surgery affected thymidine kinase activity and thymidine incorporation into DNA at specific times following partial hepatectomy. This seriously affects the interpretation of reports of experiments where the time of day of killing has been held constant and time of surgery varied. Highly significant correlation coefficients were observed for thymidine incorporation before killing versus thymidine kinase activity at time of killing and for thymidine versus orotic acid incorporation into DNA of livers from rats partially hepatectomized 2h before the end of the dark period and killed at 12h intervals. Thymidylate phosphatase activity returned to the normal amount at a rate similar to that for liver protein. Thymidylate phosphatase did not affect the validity of the thymidine kinase assay. The relationship of [(14)C]orotic acid to [(3)H]thymidine incorporation into liver DNA varied with the time of day, with the age of the rat and during the regeneration of the liver.     

A proteolytic system in growing and non-growing cells ofEscherichia coli

1. (1)
   Escherichia титр клетки содер жат протеазы Система разделения собственных белков в качестве равно как казеин с символикой (вс131) Я на несколько ще лочного рН. Темпы про теолиза не заметно влияют ethylenediaminotetraacetic кислоту или iodoacetic кисло та, п-chlormercuribenzoate снижает темп ы гидролиза (su131) Я казеи н, но ее эффект не може т быть отменено цист еина.     
   
   

Differences in chromatin proteins of growing and non-growing tissues.

The non-histone chromatin proteins of growing and non-growing tissues were compared by two-dimensional polyacrylamide gel electrophoresis. The tissues studied were normal rat liver, regenerating rat liver, thioacetamide-treated rat liver, normal rat kidney, Novikoff hepatoma and Walker 256 carcinosarcoma. Although most of the protein components were common to all of the tissues studied, the densities and sizes of spots C18, CP, C21, C25, CQ, CR, CS and CT were greater in the growing tissues than in the non-growing tissues, including the thioacetamide-treated liver. In the latter, the increased densities and sizes of spots C18, C21 and CQ are presumably related to the markedly increased nucleolar size rather than to cell division. Accordingly the increases in sizes and densities of spots C25, CP, CR, CS and CT are apparently of importance to the growth processes of normal and tumor tissues. The number of tissue specific proteins was small compared with the number of proteins in this fraction and includes BP and CBL for normal liver, BJ′ for kidney and CG′, CH′ and CP$\text{\$}\text{?}$for the tumors.     

Mechanisms of protein degradation in growing and non-growing L-cell cultures.

L-cells prelabelled with [14C]leucine and [3H]thymidine were placed in either fresh growth medium (minimal essential medium with 10% serum) or stepdown medium (minimal essential medium) for 3 days. The 14C/3H ratio remained constant in the growing cultures and decreased in the stationary-phase cultures, indicating no protein turnover in growing cultures and a degradative rate of 0.6%/h in the stationary-phase cultures. Media analysis, however, indicated that 14C-labelled proteins were being degraded at approx. 1.2%/h in growing cultures and 1.7%/h in stationary-phase cultures. Additional studies indicated that a subpopulation of L-cells in the monolayer, comprising approx. 20--30% of the total, were lost in the original processing procedure. Experiments in which recoveries approached 100% by fixation of the monolayer in situ indicated that a protein-degrading subpopulation accounted for all the observed proteolysis in the growing cultures. Proteolysis in these cultures was only partially inhibited with NH4Cl, indicating that only a small part of the protein degradation was occurring in an activated lysosomal-autophagic system. NaF produced a more effective inhibition of proteolysis, but we were not able to distinguish whether this effect was on an ATP-requiring basal-turnover mechanism or a direct effect on unregulated activity of proteinases in the cell hyaloplasm. However, NH4Cl inhibited the proteolysis induced when cells were placed in stepdown medium, suggesting that the induced proteolysis was occurring via the autophagic system. We conclude that L-cells exist in at least two states with respect to protein degradation: (a) a subpopulation that is actively replicating and does not degrade cellular proteins, and (b) a second subpopulation of cells, derived from the preceding one, which degraded most of their labelled proteins, are not capable of further replication, and are not sedimented in an iso-osmotic EDTA buffer solution. In addition, proliferating L-cells, when placed in stepdown medium, begin to degrade cell protein through a mechanism involving autophagolysosomes.     

Water permeability differs between growing and non-growing barley leaf tissues

A pressure probe technique and an osmotic swelling assay were used to compare water transport properties between growing and non-growing tissues of leaf three of barley. The epidermis was analysed in planta by pressure probe, whereas (predominantly) mesophyll protoplasts were analysed by osmotic swelling. Hydraulic conductivity (Lp) and, by implication, water permeability (Pf) of epidermal cells was 31% higher in the leaf elongation zone (Lp=0.5+/-0.2 microm s-1 MPa-1; Pf=65+/-25 microm s-1; means+/-SD of n=17 cells) than in the, non-growing, emerged leaf zone (Lp=0.4+/-0.1 microm s-1 MPa-1; Pf=50+/-15 microm s-1; n=24; P<0.05). Similarly, water permeability of mesophyll protoplasts was by 55% higher in the elongation compared with emerged leaf zone (Pf=13+/-1 microm s-1 compared with 8+/-1 microm s-1; n=57 and 36 protoplasts, respectively; P<0.01). Within the leaf elongation zone, a small population of larger-sized protoplasts could be distinguished. These protoplasts, which originated most likely from parenchymateous bundle sheath or midrib parenchyma cells, had a three-fold higher water permeability (P<0.001) as mesophyll protoplasts. The effect on Lp and Pf of known aquaporin inhibitors was tested with the pressure probe (Au+, Ag+, Hg2+, phloretin) and the osmotic swelling assay (phloretin). Only phloretin, when applied to protoplasts in the swelling assay caused an average decrease in Pf, but the effect varied between isolations. Technical approaches and cell-type and growth-specific differences in water transport properties are discussed.     

Amino acid concentrating ability of slowly growing autochthonous hepatomas and host livers.

To examine whether an increase in the intracellular concentration of amino acids always accompanies the development of a neoplasm, slowly growing autochthonous hepatomas (originating in the place where found) were induced by feeding 0.02% acetylaminofluorene followed by 0.05% phenobarbital to Buffalo strain rats. It was found that the resulting hepatomas (123 from 43 animals) concentrated less than one half the amount of non-metabolizable alpha-aminoisobutyric acid (AIB) than did the respective host and control livers when AIB was injected 24 hrs before sacrifice. While an increase in the ability to concentrate amino acids may be necessary for rapid growth, it is not a concomitant of neoplastic transformation. The narrow range of AIB concentrations found among these 123 autochthonous tumors compared to a wide spectrum of AIB concentrations found in several transplantable Morris hepatoma lines suggests that these tumors are at one of the earliest stages of their progression.     

Ribonucleic acid labelling perfused livers of protein-fed and protein-deprived rats

Several observations suggest an increased RNA synthesis in livers of protein-deprived rats, though the RNA/DNA ratio is decreased. A number of hormones may be involved in these changes. Therefore, we studied in RNA metabolism in isolated perfused livers taken from protein-fed and protein-deprived rats. (3H)-orotic acid was given to the rats 2 h before liver explantation, and (14C)-orotic acid was added to the perfusate. Other rats, called controls in vivo, whose livers were not transplanted were also given (3H)-orotic acid followed by (14C)-orotic acid. The livers of these rats, which were not hormone supplemented, were labelled for the same length of times as the livers in vitro. The ratio specific RNA radioactivity/specific nucleotide radioactivity x RNA/DNA was determined and taken as a measure of the RNA synthesis per liver cell. In the controls in vivo, this ratio was significantly higher for protein-deprived than for protein-fed rats. In livers from the protein-fed rats, labelling in vitro increased significantly when growth hormone, hydrocortisone, insulin and tri-iodothyronine were added to the perfusate. Labelling was also significantly higher in these livers than in the controls in vivo. In livers from protein-deprived rats, the ratio in question was the same whether the hormones were added to the perfusate or not, and was significantly lower than in the controls in vivo. Differences in RNA labelling are thus obtained in our in vitro system. Gel electrophoresis of RNA demonstrated normal RNA labelling, showing that the system is suitable for studying liver RNA synthesis. Further refinement can be made by studying the labelling of UTP and CTP. The results might suggest that the liver from a protein-fed rat, explanted in vitro, may increase its RNA synthesis under the influence of the four hormones in question, and that the RNA synthesis of the liver of a protein-deprived rat is high in-vivo and that it might decrease, when it is explanted to in vitro conditions.     

Ultrastructural differences between wall apices of growing and non-growing hyphae ofSchizophyllum commune

Summary Newly synthesized chitin at the hyphal apex ofSchizophyllum commune was shown to be highly susceptible to chitinase degradation and solubilization by dilute mineral acid. With time this chitin became gradually more resistant to these treatments. With a combination of the shadow-cast technique and electron microscopic autoradiography it could be shown that this process occurred as the newly synthesized chitin moved into subapical parts of growing hyphae but also in non-growing apices which had ceased growth after incorporation of theN-acetyl[6-³H]glucosamine. These results are in agreement with a model which explains apical morphogenesis by assuming that the newly synthesized wall material at the apex is plastic due to the presence of individual polymer chains but becomes rigidified because of subsequent physical and chemical changes involving these polymers.Dedicated to Dr. A.Quispel, Professor of Botany at the University of Leiden, on occasion of his retirement.     

The fine structure of growing and non-growing whole glia cell preparations.

Human glia cells become blocked in G1 if starved of serum. The characteristics of the GI blocked state are flattening on the substrate, and absence of cell translocation, ruffling and macropinocytosis. Re-entry into the cell cycle, as a result of growth factor stimulation, is accompained and even preceded by the return of this cellular locomotion. We have studied the fine structure of intact human glia cells and ultrathin sections of these cells when proliferating normally in vitro, when starved of serum and during their return to the cell cycle following stimulation with mEGF (mouse epidermal growth factor). Particular attention was paid to morphologically definable components of the cellular musculoskeletal system. Proliferating interphase glia generally had a leading lamella containing few organelles and oriented bundles of 7 nm microfilaments with structureless lamellipodia at their tips, which often formed ruffles. The perinuclear area was thick and contained many cell organelles, including mitochondria and secondary lysosomes. Glia starved of serum were thinly spread; their peripheral cytoplasm was filled with a diffuse mat of microfilaments, they had no structureless lamellipodia and their perinuclear areas, although thinner, contained cell organelles in equal amounts and of similar type of those found in proliferating cells. On EGF stimulation, after approximately 2 hours the perinuclear area of the cells thickened, and structureless lamellipodia subsequently appeared at the tips of the leading lamellae, forming ruffles. The cells finally began to translocate, the process being accompained by the reorientation and packing of the microfilaments into bundles. As the kinetics of EGF binding and break down by glia cells are similar to those described for fibroblasts, the findings do not support the concept of EGF receptor interactions inducing ultrastructurally demonstrable microfilament or other musculoskeletal structural changes in the cell. They do, however, define the differing cellular morphologies of motile and immobile structures.     

The specific activity of aldolase in the livers of old and young rats.

The catalytic activity of liver fructose-biphosphate aldolase (EC 4.1.2.13) of young and old rats in units per manomole sequence has been calculated. No evidence of the accumulation with age of altered enzyme molecules of low catalytic activity was obtained. This is contrary to results obtained using mice and rabbits and indicates that the accumulation of altered enzymes may not always be associated with aging. The possibility that altered proteins are formed, but do not accumulate, cannot be ruled out.     

Interaction between zinc and calcium in skeletal muscle in young growing rats

The purpose of the present study was to determine whether zinc and calcium could interact at the tissue level. In the first part of the study, adult rats were injected with ZnCl₂ dissolved in a physiological saline solution to determine the effects of Zn on Ca levels in various tissues. In the second part of the study, weaned rats (at day 22 postnatally) were fed a diet supplemented with Zn until day 50 and were then sacrificed. In both instances, blood, brain, heart, liver, and skeletal muscle were taken and analyzed. In the Zn-injected group, the brain, heart, and liver showed no interaction between Zn and Ca. The skeletal muscle, in contrast, showed a decrease in Ca in the homogenate, whereas Zn contents showed a significant increase at the sarcoplasmic reticulum (SR). Likewise, in the Zn-supplemented group, the Zn content of the SR vesicle of the skeletal muscle showed an increase, whereas Ca content of the pellet (14,000 g), which contains cell debris, nucleus, mitochondria, and SR vesicles of this group, showed a decrease. Current findings suggest antagonistic effects between Zn and Ca on this tissue. Zn may play a critical role in cellular function through the alteration of itnracellular distribution of Ca in skeletal muscle.