Search PubMed⌕ Search

Biomedical subjects

T G Cooper

Publications and source records attributed to T G Cooper.

At least 253 records · Page 14Linked to original sources
PubMed1980

Epithelial structure of the rat cauda epididymidis after luminal perfusion.

When solutions containing high concentrations of sodium ions (c. 140 mM) were perfused for up to 6 h through the lumen of the cauda epididymidis of the anaesthetised rat, distended spaces were consistently seen between the epithelial cells, water resorption was measurable, and clear cells lacked large clear apical vacuoles. Lowering the sodium ion concentration decreased water resorption, and distended intercellular channels were absent. Under these conditions clear cells had abnormally large or numerous pale staining vacuoles. When physiological concentrations of sodium (20 mM) and potassium (50 mM) ions were perfused, a more normal epithelium was present; intercellular channels were absent, and water was either resorbed or secreted at low rates. Clear cells appeared normal initially, but had abnormal appearance after longer periods of perfusion.

Animals↗
PubMed1979

A cluster of three genes responsible for allantoin degradation in Saccharomyces cerevisiae.

Mutant strains of Saccharomyces cerevisiae unable to utilize allantoin as sole nitrogen source were isolated and divided into three groups on the basis of their biochemical and genetic characteristics. The three loci associated with these mutant classes were designated dal1 (allantoinase minus), dal2 (allantoicase minus) and dal4 (allantoin transport minus). All three loci are located in a cluster that is proximal to the lys1 locus on the right arm of chromosome IX. The gene order and intergenic distances were estimated to be: dal1--2.5 cM--dal4--1.9cM--dal2--4.6cM-lys1.

Allantoin↗
PubMed1979

Addition of basic amino acids prevents G-1 arrest of nitrogen-starved cultures of Saccharomyces cerevisiae.

Arginase-minus mutants of Saccharomyces cerevisiae were arrested in growth and accumulated at the unbudded G-1 stage of the cell cycle when starved for nitrogen. If, however, arginine was added to the culture medium at the time of starvation, growth ceased but the cells did not collect at the unbudded G-1 stage. We suggest that arginine addition prevented the cells from collecting at the G-1 stage by starving them for histidine and lysine, thereby inhibiting synthesis of proteins needed to complete the cell cycle.

Arginase↗
PubMed1979

Oxalurate transport in Saccharomyces cerevisiae.

Oxalurate, the gratuitous inducer of the allantoin degradative enzymes, was taken into the cell by an energy-dependent active transport system with an apparent Km of 1.2 mM. Efflux of previously accumulated oxalurate was rapid, with a half-life of about 2 min. The oxalurate uptake system appears to be both constitutively produced and insensitive to nitrogen catabolite repression. The latter observations suggest that failure of oxalurate to bring about induction of allophanate hydrolase in cultures growing under repressive conditions does not result from inducer exclusion, but rather from repression of dur1,2 gene expression.

Allantoin↗
PubMed1979

Allantoate transport in Saccharomyces cerevisiae.

Allantoate uptake appears to be mediated by an energy-dependent active transport system with an apparent Michaelis constant of about 50 microM. Cells were able to accumulate allantoate to greater than 3,000 times the extracellular concentration. The rate of accumulation was maximum at pH 5.7 to 5.8. The energy source for allantoate uptake is probably different from that for uptake of the other allantoin pathway intermediates. The latter systems are inhibited by arsenate, fluoride, dinitrophenol, and carboxyl cyanide-m-chlorophenyl hydrazone, whereas allantoate accumulation was sensitive to only dinitrophenol and carboxyl cyanide-m-chlorophenyl hydrazone. Efflux of preloaded allanotate did not occur at detectable levels. However, exchange of intra- and extracellular allantoate was found to occur very slowly. The latter two characteristics are shared with the allantoin uptake system and may result from the sequestering of intracellular allantoate within the cell vacuole. During the course of these studies, we found that, contrary to earlier reports, the reaction catalyzed by allantoinase is freely reversible.

Allantoin↗
PubMed1979

Investigation by luminal perfusion of the transfer of compounds into the epididymis of the anaesthetized rat.

Controlled perfusion through the lumen of the distal cauda epididymidis in the anaesthetized rat has been explored as a means of examining physiological exchanges from blood across the epididymal epithelium. The mean length of the perfused, sperm-free, tubule was 14.5 cm (+/- 1.5 s.e.m., n = 9). No cholesterol, protein or sialic acid was detected in the perfusate at flow rates exceeding 10 microliters/min, but at rates of 0.4--1.2 microliters/min, protein appeared at concentrations of 0.21--0.55 mg/ml (i.e. secretion rates of 0.21--0.83 micrograms/min; 3 rats). Glucose was detected at all perfusion rates (3--27 microliters/min) at concentrations of 0.06--0.58 mM (0.8--6.8% blood levels). During intravenous infusions of 3H2O, radioactivity in the perfusate rapidly attained 87% blood plasma concentrations; no radioactivity was detected when carboxy-E114C]dextran or methoxy-[3H]inulin were infused. Radioactivity appeared in the epididymal perfusate to 1--7% of blood levels during intravenous infusions of D-E1U-1RC]glucose or 3-O-methyl[1-3H]glucose. This evidence suggests that the preparation is physiological and could be used to explore the dynamics of exchanges between blood and epididymis.

Animals↗
PubMed1979

Factors affecting the entry of testosterone into the lumen of the cauda epididymidis of the anaesthetized rat.

When [3H]testosterone was infused into the general circulation of the rat, perfusion of a length of the cauda epididymidis (17 +/- 1.0 (s.e.m.) cm, n = 36) with perfusates of varied composition revealed a low entry of radioactivity (1--10% plasma levels; 10 exps) with protein-free perfusates, and a greater entry (15--48%; 10 exps) when the perfusate contained bovine serum albumin (38 mg/ml). When the perfusate contained ovine or rat testicular fluid, or rat epididymal fluid at protein concentrations of 3 mg/ml or less, the entry of radioactivity into the epididymis was greater than when the perfusate contained 3 mg BSA/ml. The addition of ovine rete testis fluid protein (3 mg/ml to BSA (38 mg/ml) in the perfusate increased the uptake of radioactivity (58--106%; 6 exps). Radioactivity in blood was principally associated with testosterone (90, 95% total blood activity, 2 rats), whereas both [3H]testosterone (37, 41% total perfusate activity) and [3H]dihydrotestosterone (42, 63% total perfusate activity) was present in BSA-containing perfusates. The proportion of dihydrotestosterone appeared to increase when the perfusate contained protein of testicular origin.

Animals↗
PubMed1978

Factors influencing the observed half-lives of specific synthetic capacities in Saccharomyces cerevisiae.

We have identified a variety of factors affecting the stability of allophanate hydrolase-specific and gross cellular protein synthetic capacities. These synthetic capacities have been extrapolated by many laboratories to represent functional messenger RNAs. Synthetic capacity turnover rates that we measured were greater in diploid organisms than in haploid strains and were proportional to the temperature of the culture medium. The stability of allophanate hydrolase-specific synthetic capacity was not influenced by alterations in the nitrogen source provided in the culture medium, but was increased up to 15-fold by the total inhibition of protein synthesis. Cultures in which protein synthesis was inhibited as little as 20% exhibited hydrolase-specific synthetic capacities more than 2-fold greater than those observed in the absence of inhibition.

Allophanate Hydrolase↗
PubMed1978

Gross and histological variations along the length of the rat vas deferens.

The gross morphology of the vas deferens of the rat and the changes that occur along its length are reported. It is shown that the organ can be divided into proximal, distal and terminal portions. Each portion is histologically unique and is situated in a different part of the body. The differences are discussed in relation to the function of the organ and their possible role in the consequences of vasectomy.

Animals↗
PubMed1978

Basic amino acid inhibition of cell division and macromolecular synthesis in Saccharomyces cerevisiae.

Growth of Saccharomyces cerevisiae on poor nitrogen sources such as allantoin or proline was totally inhibited by addition of a non-degradable basic amino acid to the medium. Cells treated with lysine contained greatly reduced quantities of histidine and arginine. Conversely, lysine and histidine were severely reduced in arginase-deficient cells treated with arginine. When all three basic amino acids were present in the culture medium, growth was normal suggesting that synthesis of all three basic amino acids was decreased by an excess of any one of them. Inhibition of growth was accompanied by a fivefold increase in the observed ratio of budded to unbudded cells. These morphological changes suggested that DNA synthesis was inhibited. Consistent with this suggestion, addition of a basic amino acid to the culture medium substantially reduced the ability of the cells to incorporate [14C]uracil into alkali-resistant, trichloroacetic acid-precipitable material. RNA and protein synthesis, although decreased, were less sensitive to the effects of such additions.

Arginine↗
PubMed1978

Metabolite compartmentation in Saccharomyces cerevisiae.

Uninduced cultures of Saccharomyces cerevisiae exhibit high basal levels of allantoinase, allantoicase, and ureidoglycolate hydrolase, the enzymes responsible for degrading allantoin to urea. As a result, these activities increase only 4- to 8-fold upon induction, whereas the urea-degrading enzymes, urea carboxylase and allophanate hydrolase, have very low basal levels and routinely increase 30-fold on induction. Differences in the inducibility of these five enzymes were somewhat surprising because they are all part of the same pathway and have the same inducer, allophanate. Our current studies reconcile these observations. S. cerevisiae normally contained up to 1 mM allantoin sequestered in a cellular organelle, most likely the vacuole. Separation of the large amounts of allantoin and the enzymes that degrade it provide the cell with an efficient nitrogen reserve. On starvation, sequestered allantoin likely becomes accessible to these degradative enzymes. Because they are already present at high levels, the fact that their inducer is considerably removed from the input allantoin is of little consequence. This suggests that at times metabolite compartmentation may play an equal role with enzyme induction in the regulation of allantoin metabolism. Metabolism of arginine, another sequestered metabolite, must be controlled both by induction of arginase and compartmentation because arginine serves both as a reserve nitrogen source and a precursor of protein synthesis. The latter function precludes the existence of high basal levels of arginase.

Allantoin↗
PubMed1978

Induction and inhibition of the allantoin permease in Saccharomyces cerevisiae.

Allantoin uptake in Saccharomyces cerevisiae is mediated by an energy-dependent, low-Km, active transport system. However, there is at present little information concerning its regulation. In view of this, we investigated the control of alloantoin transport and found that it was regulated quite differently from the other pathway components. Preincubation of appropriate mutant cultures with purified allantoate (commercial preparations contain 17% allantoin), urea, or oxalurate did not significantly increase allantoin uptake. Preincubation with allantoin, however, resulted in a 10- to 15-fold increase in the rate of allantoin accumulation. Two allantoin analogs were also found to elicit dramatic increases in allantoin uptake. Hydantoin and hydantoin acetic acid were able to induce allantoin transport to 63 and 95% of the levels observed with allantoin. Neither of these compounds was able to serve as a sole nitrogen source for S. cerevisiae, and they may be non-metabolizable inducers of the allantoin permease. The rna1 gene product appeared to be required for allantoin permease induction, suggesting that control was exerted at the level of gene expression. In addition, we have shown that allantoin uptake is not unidirectional; efflux merely occurs at a very low rate. Allantoin uptake is also transinhibited by addition of certain amino acids to the culture medium, and several models concerning the operation of such inhibition were discussed.

Allantoin↗
PubMed1978

Control of vacuole permeability and protein degradation by the cell cycle arrest signal in Saccharomyces cerevisiae.

Saccharomyces cerevisiae responds to deperivation of nutrients by arresting cell division at the unbudded G1 stage. Cells situated outside of G1 at the time of deperivation complete the cell cycle before arresting. This prompted an investigation of the source of nutrients used by these cells to complete division and the mechanisms controlling their availability. We found a close correlation between accumulation of unbudded cells and loss of previously formed allophanate hydrolase activity after nutrient starvation. These losses were not specific to the allantoin, system since they have been observed for a number of other enzymes and also when cellular protein levels were monitored with [3H]leucine. Loss of hydrolase activity was also observed when protein synthesis was inhibited either by addition of inhibitors or loss of the prtl gene product. We found that onset of nutrient starvation brought about release of large quantities of arginine and allantoin normally sequestered in the cell vacuole. Treatment of a cells with alpha-factor resulted in both the release of allantoin and arginine from the cell vacuole and the onset of intracellular protein degradation. These effects were not observed when either alpha cells or a/alpha diploid strains were treated with alpha-factor. These data suggest that release of vacuolar constitutents and protein turnover may be regulated by the G1 arrest signal.

Allophanate Hydrolase↗
PubMed1977

Vitamin K-dependent carboxylation of peptide-bound glutamate. The active species of "CO2" utilized by the membrane-bound preprothrombin carboxylase.

Vitamin K participates in the post-translational carboxylation of peptide-bound glutamate to form the gamma-carboxy-glutamate residues of prothrombin. The reaction requires reduced vitamin K, bicarbonate, oxygen, and a membrane-bound carboxylase. The active species of "CO2," i.e. CO2 or HCO3-, utilized in this carboxylation was determined by the low temperature method of Filmer and Cooper ((1970) J. Theor. Biol. 29, 131-145), taking advantage of the fact that menaquinone-2, in contrast to phylloquinone, is very active at 10 degrees. Microsomes from livers of vitamin K-deficient rats, were incubated in the presence of cycloheximide, avidin, NADH, menaquinone-2, 1 mM acetazolamide (to inhibit carbonic anhydrase), and either 14CO2 or H14CO3-. At 1-min intervals aliquots were removed from the reaction mixture. gamma-Carboxyglutamate was isolated from these samples by ion exchange chromatography after alkaline hydrolysis. After 1 min the incorporation of 14CO2 into gamma-carboxyglutamate was 8 to 10 times as great as that found with H14CO3-. When the carbonic anhydrase inhibitor was omited (with or without addition of exogenous carbonic anhydrase) the two incorporation curves approximated each other at a rate near that exhibited by bicarbonate alone. Similar results were obtained in a microsomal carboxylase system solubilized with Triton X-100. It is concluded that CO2 is the active species of "CO2" initially participating in the vitamin K-dependent carboxylation of preprothrombin and that neither ATP nor biotin is required for the reaction.

Animals↗
PubMed1977

Observations on destruction of spermatozoa in the cauda epididymidis and proximal vas deferens of non-seasonal male mammals.

The electron microscope has been used to examine luminal spermatozoa from the cauda epididymidis and proximal vas deferens of rats, mice, hamsters and guinea pigs. Free in the lumen of all species are accumulations of a dense material within which are vesicles, granules and dense bodies, as well as spermatozoa. The spermatozoa are undergoing a process of degeneration as judged by a loss of plasma membrane from both heads and tails and further disruption of acrosomal membranes, mitochondrial sheaths and outer dense fibers. Disruption of spermatozoa also occurs outside these obvious dense masses when the luminal protein precipitated by the fixation procedure has contact with the spermatozoon. Intact spermatozoa are separated from luminal material by a clear "halo".

Animals↗
PubMed1977

Phagocytosis of spermatozoa in the terminal region and gland of the vas deferens of the rat.

The existence of a discrete group of cells that are able to phagocytose spermatozoa is reported in the terminal vas deferens of the rat. In addition it is shown that phagocytosis of spermatozoa occurs in the gland of the vas deferens. The cytological mechanisms involved in the phagocytotic process are discussed, and the role that this activity may have on the removal of surplus spermatozoa is discussed.

Animals↗
PubMed1977

Regional variation in the surface morphology of the epithelium of the rat ductuli efferentes, ductus epididymidis and vas deferens.

The luminal surface of epithelial cells lining the ductuli efferentes, ductus epididymidis and first portion of the vas deferens were studied with the scanning electron microscope. In ductuli efferentes obvious ciliated cells are identified and it is shown that on non-ciliated cells the short microvilli adhere to one another to form clumps of microvilli. In the epididymis two cell types are described and can be identified as principal cells and clear cells based on the presence or absence of microvilli. Clear cells vary in number along the duct, being most numerous distally. Their surface morphology is also most variable distally. In the vas deferens, principal cells with surface microfilli are easily identified; but, in addition, a second cell type is seen, the identity of which is not known.

Animals↗