Identification and characterization of a proton pump on lysosomes by fluorescein-isothiocyanate-dextran fluorescence

Fluorescein isothiocyanate-conjugated dextran was introduced preferentially into hepatic lysosomes by intraperitoneal injection into rats. The pH in isolated lysosomes, measured by fluorescein fluorescence, was approximately 5 and gradually increased in KCl (to 7.0) at 25 degrees C. In the presence of Mg2+, ATP caused acidification of lysosomes that was reversed by the protonophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone. Mn2+, Co2+, and Fe2+ could replace Mg2+ but Ca2+ could not. Cu2+, Zn2+, and Cd2+ were inhibitory. A membrane-permeant anion, in practice chloride, was required for this acidification. ATP analogues, including 5'-adenylyl imidodiphosphate, could not be substituted for ATP. ATP-driven acidification was sensitive to N-ethylmaleimide and quercetin but insensitive to oligomycin, ouabain, and vanadate. There were some differences between "normal" lysosomes and tritosomes; the acidification was resistant to azide and N,N'-dicyclohexylcarbodiimide in normal lysosomes but sensitive to these reagents in tritosomes. These results provide evidence for the presence of an electrogenic proton pump driven by MgATP (H+-ATPase) on lysosomes.

Electron microscopic observations of experimental carbon monoxide encephalopathy in the acute phase

The cerebral and cerebellar lesions of the cats that were exposed to 0.3% carbon monoxide gas under artificial respiration were examined by an electron microscope at different intervals. During the first few days, the most outstanding features were segmental empty axonal swelling, dilatation of the extracellular space, swelling and necrosis of astrocytes and oligodendroglias, and lamellar separation of the myelin sheath predominantly in the deep cerebral white matter. These changes subsided within one week. Instead, collapsed myelin increased in number and phagocytosis of disintegrated myelin was occasionally observed. Astrocytes and oligodendroglias became prominent in size and number. Changes suggestive of selective damage of myelin or oligodendroglia was not encountered. We proposed that CO-followed by Wallerian degeneration. The pathogenesis of CO-encephalopathy was also discussed.

Restoration by cyclic AMP of the differentiated phenotype of chondrocytes from de-differentiated cells pretreated with retinoids

Parathyroid hormone (PTH) increases the cyclic AMP level in rabbit costal chondrocytes in culture. PTH, dibutyryl cyclic AMP (DBcAMP), and 8-bromo cyclic AMP (8-Br cAMP)induce ornithine decarboxylase (ODC) and expression of the differentiated phenotype of chondrocytes in this cell system. On the other hand, retinoids inhibit expression of the differentiated phenotype of chondrocytes. In the present study, the effects of PTH, DBcAMP, and 8-Br cAMP on rabbit costal chondrocytes pretreated with retinoids were examined. PTH did not increase the cellular cyclic AMP level in de-differentiated cells that had been pretreated with retinyl acetate or retinoic acid for three days, but it did increase the cyclic AMP level four days after removal of retinoids. PTH did not stimulate ODC activity or expression of the differentiated phenotype of chondrocytes in the de-differentiated state. On the other hand, DBcAMP or 8-Br cAMP stimulated expression of the differentiated phenotype of chondrocytes even in de-differentiated cells, as judged by morphological and histological changes of the cells and increase in glycosaminoglycan synthesis. Cyclic AMP analogues also induced ODC in these cells.

The molecular structure of d(ICpCpGpG), a fragment of right-handed double helical A-DNA

The DNA tetramer d(ICpCpGpG) or ICCGG crystallizes as a double-stranded 4-base pair (bp) segment of an A helix. Two such tetramer helices are packed together in the crystal with local helix axes nearly coincident, simulating an 8-bp helix, and four such octamers make up the tetragonal unit cell. Restrained energy and reciprocal space refinement has led to an R factor of 20.5% at 2.1 A resolution. The ICCGG helix has a twist corresponding to 10.7 bp per turn, a 19 degree base tilt and a 2.3 A rise per base pair along the helix axis. The mean propeller twist of 18 degree is comparable with, and has the same rotational sense as that observed in the B-DNA dodecamer CGCGAATTCGCG at similarly high alcohol concentration. Backbone phosphate groups in A-DNA are extensively hydrated, including a network across the opening of the major groove, whereas base edge N and O groups in major and minor grooves are less hydrated than in B-DNA. The minor groove spine of hydration observed in B-DNA is totally absent. These observations of relative hydration confirm and extend the model for the B- to A- helix transition proposed earlier on the basis of the B helix structure.

Tocofibrate (tocopheryl 2-(p-chlorophenoxy) isobutyrate); a new peroxisomotropic compound, and its hypocholesterolemic activity in cholesterol-fed rats

The effect of tocofibrate (tocopheryl 2-(p-chlorophenoxy) isobutyrate) on cholesterol levels in rats fed a high-fat cholesterol diet was investigated. The efficacy of tocofibrate in reducing blood cholesterol levels was comparable to that of clofibrate, a compound with known hypocholesterolemic activity. To investigate further the mechanism underlying the action of tocofibrate, the intracellular distribution of the compound in liver was examined. The results indicate that the distribution of tocofibrate clearly differs from that of both clofibrate and alpha-tocofibrate is primarily associated with its effect upon liver peroxisomes.

Comparative study on pathogenesis of selective cerebral lesions in carbon monoxide poisoning and nitrogen hypoxia in cats

Since in a previous study hypoxia and subsequent hypotension were considered to be essential for the pathogenesis of carbon monoxide encephalopathy (CO-encephalopathy), experiments were conducted to see whether a combination of nitrogen hypoxia and subsequent systemic hypotension of similar degree and duration as in the previous experimental CO poisoning could induce the same lesion in the CNS of cats. The partial pressure of blood oxygen was reduced to less then 26 mm Hg by increasing the concentration of nitrogen in N2/O2 gas to be inhaled in 1.5h and then the aortic blood pressure (BP) was reduced to 60-80 mm Hg by blood depletion and ganglion-blockage for 1h. In 11 of the 15 cats, lesions were produced in the CNS which were similar by light and electron microscopy to those in CO-encephalopathy. In control groups which were treated by hypoxemia only, hypotension only or a combination CO2-gas inhalation and hypotension without hypoxemia, such lesions were not found in the cerebral white matter. Considering the pathogenesis of lesions in the cerebral white matter in both nitrogen hypoxia and CO-poisoning, two factors i.e., hypoxemia and subsequent systemic hypotension, are common and essential. Further, the enormous vasodilatation in the cerebral white matter induced by hypoxemia and subsequent drop in BP seem to cause a more severe circulatory disturbance in the cerebral white matter than in the cortex.

Structure of the baboon endogenous virus genome: nucleotide sequences of the long terminal repeat

The entire nucleotide sequence of the long terminal repeat (LTR) of baboon endogenous virus (BaEV) M7 was determined, which consisted of 554 base pairs (bp). At both ends of the LTR, 13 bp sequences, AAATGAAAAGTAA and TGATTCTAACATC, were detected to be inverted repeats. The structure with these inverted repeats resembles those of other retroviruses and transposable elements. a Hogness box, TATAAAA, and a putative poly(A)-addition signal, AGTAAA, were present within the right-hand half of the LTR, where the initiation and termination of the viral RNA synthesis seems to occur in the integrated BaEV genome. The primer-binding site of at least 14 bp long was found just outside of the LTR where the strong stop DNA started, and the primer for reverse transcription in BaEV seemed to be tRNAPro. Several structural features are commonly detected in the LTRs of BaEV and other retroviruses. Our studies suggest that BaEV has evolved from a common ancestor with other mammalian type C viruses. Close relationships between BaEV and a feline endogenous virus, RD114, are demonstrated.

Role of polyamines in expression of the differentiated phenotype of chondrocytes in culture

Addition of putrescine to cultures of rabbit costal chondrocytes during the log-phase stimulated expression of their differentiated phenotype, as judged by increase in the synthesis of glycosaminoglycans and of metachromasia with toluidine blue staining. Putrescine stimulated glycosaminoglycan synthesis maximally at a concentration of 10(-7) M, and spermidine and spermine were also effective at similar concentration. These polyamines had little effect on DNA synthesis, RNA synthesis, DNA accumulation, or protein accumulation. These findings suggest that polyamines may be important in the expression of the differentiated phenotype of chondrocytes in culture.

Dose responses of five hepatocarcinogens for the initiation of rat hepatocarcinogenesis

Using the Solt and Farber model (Nature, 263 (1976) 701), dose-response relationships between initiating agents and the induction of hyperplastic nodules in rat liver were investigated. Male Fischer 344 rats were initiated by a single application of 1 of 5 carcinogens at 3 doses: 200.0, 50.0 and 12.5 mg/kg of diethylnitrosamine (DEN); 1.00, 0.25 and 0.062 mg/kg of aflatoxin B1 (Af-B1); 60.0, 15.0 and 3.75 mg/kg of N-2-fluorenylacetamide (2-FAA); 600.0, 150.0 and 37.5 mg/kg of 3'-methyl-4-dimethylaminobenzene (3'-me-DAB); 40.0, 10.0 and 2.5 mg/kg of dimethylnitrosamine (DMN) and their vehicles. Two weeks after initiation, animals were placed on a 0.02% 2-FAA diet for 2 weeks. Partial hepatectomy was performed at the end of the third week of the experiment. All rats were killed 4 weeks after the initiation, and the hyperplastic nodules of the liver were counted and their areas measured. Dose responses were observed in both numbers and areas of hyperplastic nodules per unit area of sections with all of the 5 carcinogens examined.

Direct effects of carbon monoxide on cardiac function

The direct effects of carbon monoxide (CO) on cardiac function were investigated in hemoglobin-free living rabbits treated with perfluorochemical blood substitutes. After exchange transfusion with a perfluorochemical emulsion, the erythrocyte count was below 10 X 10(4)/mm3 in each animal. Gas mixtures of oxygen with 5%, 10%, and 20% of CO or nitrogen were administered via a respirator. The results showed that the cardiac effects of CO and nitrogen were significantly different as regards changes in arterial pressure, pulse pressure, heart rate, and the product of heart rate and systolic arterial pressure in spite of the same oxygen tension in the inhaled gases. It was concluded that there was a direct effect of CO not mediated by hemoglobin.

Purification and properties of rabbit liver acid-lipase (4-methylumbelliferyl oleate hydrolase)

An acid lipase was purified from rabbit liver lysosomes by, in sequence, osmotic treatment of the lysosomal fraction, Sephadex LH-20, DEAE-Sephadex A-50, Bio-Gel A-5m, hydroxyapatite and, finally, Sephadex G-200 column chromatography. The substrate was 4-methylumbelliferyl oleate. The enzyme was solubilized by Sephadex LH-20 column chromatography instead of detergents and organic solvents, to obtain an intrinsic macromolecule. 4-Methylumbelliferyl oleate hydrolase, osmotically released from lysosomal particles, had a very high molecular weight (greater than 800 000) which was reduced by gel filtration on a Sephadex LH-20 column; the final molecular weight of the purified enzyme was 58 000. The specific activity of 4-methylumbelliferyl oleate hydrolase increased at almost the same rate as acid cholesterol esterase and triacylglycerol lipase after Sephadex LH-20 column chromatography; the thermal stability of the activity of the three enzymes was almost identical. We also discuss the properties of the enzyme molecule and the interaction between the enzyme and the lysosomal membrane.

Structure of the baboon endogenous virus genome: cloning of circular virus DNA in bacteriophage lambda

Linear, small and large circular forms of unintegrated viral DNAs were detected in Hirt supernatant fraction of human cultured cells infected with baboon endogenous virus M7. The circular M7 DNAs were cloned in bacteriophage lambda, Charon 28. Seventeen independent clones were isolated and analyzed by restriction endonuclease mapping. Nine clones were carrying a viral sequence of 8.6 kilobase pairs (kb) with two tandem repeats of 0.6 kb, which correspond to the large circular form of the unintegrated M7 DNA. Eight other clones had the viral insert of 8.0 kb, i. e., the small circular form, and were deleted one of the repeated sequences. The repeated sequences correspond to the long terminal repeats of 0.6 kb, located at both ends of the linear M7 DNA of 8.6 kb. One of the recombinants of the large circular M7 DNA had an inversion of 2.5 kb. One end of the inverted sequence was near the terminus of the long terminal repeats and the other in the gag gene region. The inversion seems to be occurred by integration of a viral DNA within itself during early periods of infection. The mechanism of the processes leading to integration is discussed from the structure of these unintegrated M7 DNAs as the precursors.

Structure of a B-DNA dodecamer: conformation and dynamics

The crystal structure of the synthetic DNA dodecamer d(CpGpCpGpApApTpTpCpGpCpG) has been refined to a residual error of R = 17.8% at 1.9-A resolution (two-sigma data). The molecule forms slightly more than one complete turn of right-handed double-stranded B helix. The two ends of the helix overlap and interlock minor grooves with neighboring molecules up and down a 2(1) screw axis, producing a 19 degrees bend in helix axis over the 11-base-pair steps of the dodecamer. In the center of the molecule, where perturbation is least, the helix has a mean rotation of 36.9 degrees per step, or 9.8 base pairs per turn. The mean propeller twist (total dihedral angle between base planes) between A . T base pairs in the center of the molecule is 17.3 degrees, and that between C . G pairs on the two ends averages 11.5 degrees. Individual deoxyribose ring conformations as measured by the C5'-C4'-C3'-O3' torsion angle delta, exhibit an approximately Gaussian distribution centered around the C1'-exo position with delta avg = 123 degrees and a range of 79 degrees to 157 degrees. Purine sugars cluster at high delta values, and pyrimidine sugars cluster at lower delta. A tendency toward 2-fold symmetry in sugar conformation about the center of the molecule is detectable in spite of the destruction of ideal 2-fold symmetry by the molecular bending. More strikingly, sugar conformations of paired based appear to follow a "principle of anticorrelation," with delta values lying approximately the same distance to either side of the center value, delta = 123 degrees. This same anticorrelation is also observed in other DNA and DNA . RNA structures.

Effects of parathyroid hormone and cyclic AMP analogues on the activity of ornithine decarboxylase and expression of the differentiated phenotype of chondrocytes in culture

Parathyroid hormone (PTH) greatly increased the level of adenosine 3', 5' cyclic monophosphate (cAMP) in rabbit costal chondrocytes in culture 2 minutes after its addition. PTH, as well as N6 O2' dibutyryl adenosine 3', 5' cyclic monophosphate (DBcAMP) and 8 Bromo adenosine 3', 5' cyclic monophosphate (8 Br-cAMP) induced ornithine decarboxylase (ODC; L-ornithine carboxylyase; EC 4.1.1.17), which reached a maximum 4 hours after their addition. Neither cAMP, N6 O2' dibutyryl guanosine 3', 5' cyclic monophosphate (DBcGMP), nor sodium butyrate increased the activity of the enzyme. PTH had no effect on DNA synthesis, while DBcAMP and 8 Br-cAMP decreased DNA synthesis. Expression of the differentiated phenotype of chondrocytes in culture was also induced by PTH, DBcAMP, and 8 Br-cAMP, but not by cAMP, DBcGMP, or sodium butyrate, as judged by morphological change. Glycosaminoglycan synthesis, a characteristic of the cartilage phenotype, began to increase 8 hours after addition of PTH or DBcAMP, reaching a plateau 32 hours after their addition. These findings suggest that PTH induces increase of ODC activity and expression of the differentiated phenotype of chondrocytes through increase of cAMP and that induction of OCD is closely related to expression of the differentiated phenotype of chondrocytes.

A sequential quantitative study of the reversibility or irreversibility of liver hyperplastic nodules in rats exposed to hepatocarcinogens

The behavior of hyperplastic nodules following an in vivo short-term screening test for hepatocarcinogens was studied. Rats were injected ip with 200 mg/kg body weight of diethylnitrosamine (DEN), given basal diet containing 200 ppm of N-2-fluorenylacetamide (2-FAA) (group 1), 1000 ppm of the alpha-isomer of 1,2,3,4,5,6,-hexachlorocyclohexane (alpha-BHC) (group 2) or basal diet (group 3) from week 3 to week 8, and then given basal diet and tap water. They were subjected to partial hepatectomy at the end of week 3. Animals were killed at weeks 4, 6, 8, 10, 20, 30, 40, and 50. A significant disappearance of hyperplastic nodules following the cessation of carcinogen treatment was observed in group 1, but was not evident in groups 2 and 3. With gamma-glutamyltranspeptidase (GGTase) as a positive marker and adenosine triphosphatase (ATPase) as a negative marker, hyperplastic nodules were classified into 3 different phenotypic categories, i.e., (1) GGTase-positive and ATPase-negative, (2) GGTase-positive, and (3) ATPase-negative. The percentages of GGTase-positive and ATPase-negative hyperplastic nodules were almost 80 approximately 90% in group 1 and 70 approximately 80% in groups 2 and 3. Some of the hyperplastic nodules were necrotic from week 8 in groups 1 and 2, and from week 20 in group 3. Subsequently, the numbers of necrotic hyperplastic nodules increased with time. Hepatocellular carcinomas were found at weeks 30, 40, and 50 in group 1, and at weeks 40 and 50 in group 2. Significantly higher incidences of cancer were found in group 1 than in group 2. The hepatocellular carcinomas were also classified enzyme-histochemically into 3 different phenotypic categories as for hyperplastic nodules, but the percentage (20%) of GGTase-positive and ATPase-negative hepatocellular carcinomas was significantly lower than that (70 approximately 90%) of GGTase-positive and ATPase-negative hyperplastic nodules in each group.

The effects of various chemicals on the development of hyperplastic liver nodules in hepatectomized rats treated with N-nitrosodiethylamine or N-2-fluorenylacetamide

The effects of various hepatocarcinogenic, non-hepatocarcinogenic and non-carcinogenic chemicals on the induction of hyperplastic liver nodules by N-nitrosodiethylamine (DEN) or N-2-fluorenylacetamide (2-FAA) as an initiator were studied in male Fischer 344 rats. Rats were injected intraperitoneally with 200 mg of DEN/kg body weight or were fed on basal diet containing 200 ppm of 2-FAA for 2 weeks, and then given various test chemicals starting from week 3. They were also partially hepatectomized in week 3. All animals were killed at the end of week 8 and examined histologically. For quantitative analysis, hyperplastic nodules in the liver were measured with a color video image processor, VIP-21C. The effect of various chemicals in rats treated with DEN or with 2-FAA were compared. The production of hyperplastic liver nodules was greatest in rats treated with strong hepatocarcinogens, and less in rats treated with weak hepatocarcinogens. Very few hyperplastic nodules were produced after treatment with non-hepatocarcinogens or noncarcinogens. Hyperplastic nodules were formed in rats treated with phenobarbital, which is a hepatopromoter. Saccharin, which is a urinary bladder promoter, did not enhance the production of hyperplastic nodules in the liver. These results indicate that many hepatocarcinogens enhance liver carcinogenesis. The classification of chemicals as liver carcinogens is discussed on the basis of the results.

Redox conformation changes in refined tuna cytochrome c

Tuna ferrocytochrome c and ferricytochrome c have been refined independently at high resolution (1.5 A and 1.8 A) to crystallographic residual errors of 17.3% and 20.8%, respectively. Small but significant conformational differences are seen surrounding a buried water molecule that is hydrogen bonded to Asn-52, Tyr-67, and Thr-78. In the oxidized state, this water molecule is 1.0 A closer to the heme and the heme has moved 0.15 A out of its heme crevice; both changes lead to a more polar microenvironment for the heme. Chemical modification studies, patterns of evolutionary conservatism, structural differences in bacterial cytochromes, and x-ray studies all agree that the "active site" for cytochrome c is bounded by lysines 8, 13,27, 72, 79, 86, and 87 (thus containing the evolutionary conservative 72-87 loop) and has the buried water molecule just below its surface and the opening of the heme crevice slightly to one side.

Crystal structure analysis of a complete turn of B-DNA

DNA is probably the most discussed and least observed of all biological macromolecules. Although its role in biology is a central one, with many examples such as operators and restriction sites where specific base sequences have control functions or interact with specific enzymes, the structures that DNA can adopt have been based until now only on sequence-averaged fibre diffraction patterns. Recent improvements in triester synthesis methods have made possible the preparation of sufficient homogeneous DNA of predetermined sequence for crystallization and X-ray structure analysis. We report here the first single-crystal structure analysis of more than a complete turn of right-handed B-DNA, with the self-complementary dodecamer sequence d(CpGpCpGPApApTpTpCpGpCpG) or CGCGAATTCGCG.

Internal mobility of ferrocytochrome c

In the refinement of the X-ray diffraction structures of molecules, it is conventional to introduce atomic 'temperature factors' of the Debye-Waller form to characterize the widths of the electron density peaks corresponding to the atoms. Although these factors are known to include a variety of contributions other than thermal fluctuations of the atomic positions, recent progress in the refinement of protein structures has led to inferences concerning atomic mobilities from the temperature factor data for several proteins. Atomic position fluctuations can be calculated independently by the molecular dynamics method, in which the classical equations of motion for the atoms of an equilibrated protein are solved on a computer. We now show that the X-ray diffraction and dynamical simulation methods yield similar pictures of the atomic mobility in tuna ferrocytochrome c.

Effect of hyperbaric oxygen on cyanide intoxication: in situ changes in intracellular oxidation reduction

To evaluate the efficacy of hyperbaric oxygen on cyanide intoxication, changes in the intracellular oxidation-reduction state of the renal cortex were observed in situ in 16 New Zealand white rabbits by detecting the reduced pyridine nucleotide fluorescence that represents the degree of cyanide blockade of the respiratory chain. The data indicated that 100% oxygen at 2 ATA exerted both prophylactic and therapeutic antagonistic effects on the cyanide poisoning. Administration of hyperbaric oxygen could constitute a significant treatment if proper chemical treatment is carried out concomitantly.

High-salt d(CpGpCpG), a left-handed Z' DNA double helix

The DNA tetramer d(CpGpCpG) or CGCG crystallizes from high-salt solution as a left-handed double helix, the Z' helix. Its structure differs from that of the other known left-handed helix, Z-DNA, by a Cl'-exo sugar pucker at deoxyguanosines rather than C3'-endo, and these represent two alternative solutions to the same steric constraint arising from the syn glycosyl bond orientation. The apparent molecular basis for the Z to Z' transition in going from intermediate to high salt is substitution of a bound anion for water at guanine amino groups, and consequent charge repulsion of anions and backbone phosphates.

Polyamine and differentiation: induction of ornithine decarboxylase by parathyroid hormone is a good marker of differentiated chondrocytes

The activity of ornithine decarboxylase (OD-Case:L-ornithine carboxy-lyase, EC 4.1.1.17) in rabbit costal chondrocytes in culture increased markedly after addition of parathyroid hormone (PTH), reaching a maximum 4 to 5 hr after PTH addition. The increase in ODCase activity was followed by increase in the intracellular concentrations of polyamines, especially putrescine, which increased in 6 hr to about 3-fold that of untreated cultures. The induction of ODCase by PTH was not observed in L, 3T3, HeLa, buffalo rat liver, or BHK cells. Retinyl acetate and retinoic acid both inhibited expression of the differentiated phenotype of chondrocytes by rabbit costal chondrocytes in culture within 3 days after their addition, as judged by morphological change and decrease in sulfate incorporation into glycosaminoglycans but did not inhibit cell proliferation. PTH could not induce an increase in ODCase in de-differentiated cells that had been pretreated with retinyl acetate or retinoic acid for 3 days. but 4 days after removal of the retinoids, these de-differentiated cells regained the ability to synthesize ODCase in response to PTH. These facts suggest that the induction of ODCase and the formation of putrescine by PTH are good markers of the differentiated phenotype of cultured chondrocytes.

The characteristics of the RNA-dependent DNA polymerase of baboon endogenous virus

The characteristics of the virion-associated RNA-dependent DNA polymerase (RDPase) of a baboon endogenous virus, M7, were studied extensively; the optimal conditions for the exogenous RDPase reaction were obtained with 0.4 mM-Mn2+, 110 mM-NaCl, 24 microgram/ml poly(rA). oligo(dT)12-18, at pH 7.6 in the presence of 0.01 % Brij-58. Under these conditions, the incorporation of 3H-TMP proceeded up to 90 min at a speed of 0.1 pmol TMP/microgram virus protein/min. Poly(rC). oligo (dG)12-18 and poly(rCm). oligo (dG)12-18 served as the template-primers in the exogenous reaction with 3 mM-Mg2+ and 0.4 mM-Mn2+, respectively. Polyuridylic acid, bleomycin, rifampicin, spermidine and inorganic phosphate significantly inhibited the RDPase activity of BaEV. The RDPase of BaEV requires a higher concentration of NaCl, a lower pH and milder conditions of detergent treatment than those of other mammalian retroviruses.

Large-scale purification of two forms of active lac operator from plasmids

A practical procedure is described for obtaining milligram quantities of a small (29 nucleotide) Eco RI restriction fragment of DNA containing the Escherichia coli lac operator. A yield of 10--15 mg of operator is obtained from 1 kg of wet cell paste. The resultant operator is shown to be homogeneous and competitively active in filter assays. Two separable but interconvertible forms of lac operator exist in solution, probably linear duplex and hairpin isomers. Only the presumed linear form is active in binding lac repressor by competition assay, but the two isomers are interconvertible by heating to 80 degrees C. The methods described here should be generally applicable for purifying other restriction fragments from plasmids.

Fine structural changes in the aging mouse thyroid

Age related changes of the thyroid gland of CF1 mice ranging in age from 15 days to 24 months were studied morphologically and biochemically. The mean diameter of follicles becomes larger with advancing age due to fusion of adjacent follicles, and there is also an increasing variability of follicle diameter. The volumetric density of lysosomes in the cytoplasm of epithelial cells lining follicles increases with age. In the younger (seven days to 1.5-month-old) mice, most lysosomes are small and homogeneously dense; these are considered to be the primary lysosomes necessary for the hydrolysis of reabsorbed colloid droplets. The heterogeneously dense, large lysosomes containing lipid-like droplets increase in number with age, especially in mice over 15 months. The specific activities of acid phosphatase, beta-glucuronidase and beta-galactosidase show a relative decrease with age after six months; although there may be an absolute increase. Some of the lysosomes observed in old animals may be residual bodies.