Autologous rosette-forming T cells as the responding cells in human autologous mixed-lymphocyte reaction

Autologous rosette-forming cells (Tar cells) have surface and functional characteristics of post-thymic precursors and among these characteristics there are some that have been identified in the responsive cell of the autologous mixed-lymphocyte reaction (AMLR). We therefore did AMLR with circulating mononuclear cells from normal subjects using as responding cells either total T cells, T cells depleted of Tar cells, or purified Tar cells. The response of Tar cells in AMLR was significantly greater than that of total T cells and these responded significantly more than Tar-depleted T cells. Conversely, Tar cells responded less than total T cells or T cells depleted of Tar cells in allogeneic mixed-lymphocyte reactions. Increasing numbers of Tar cells gave significantly greater AMLR responses both alone and when added to diminishing proportions of Tar-depleted T cells to keep the number of T cells constant in the system. Tar cells are the responding cells in AMLR but not in allogeneic mixed-lymphocyte reactions.

Heterogeneity of glutamine synthetase polypeptides in Neurospora crassa

Purified preparations of Neurospora crassa glutamine synthetase contain two nonidentical polypeptides that can be separated by acrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and 7 M urea. These polypeptides are synthesized both in vivo and in a heterologous cell-free protein-synthesizing system. The data presented indicate that both polypeptides contain an active site for glutamine synthetase activity and suggest that there is not a precursor-product relationship between them.

Glutamine metabolism in nitrogen-starved conidia of Neurospora crassa

During nitrogen deprivation, de novo synthesis of glutamine synthetase was induced in non-growing conidia of Neurospora crassa. When ammonia or glutamine was added to conidia which had been deprived of nitrogen, glutamine and arginine accumulated at a higher rate than in condia not deprived of nitrogen. The degradation of exogenous glutamine to glutamate is apparently a necessary step in the accumulation of glutamine and arginine within the conidia. In non-growing conidia, a cycle probably operates in which glutamine is degraded and resynthesized. The advantages of such a cycle would be that the carbon and nitrogen could be used to synthesize amino acids in general, as well as for the synthesis and accumulation of arginine and/or glutamine in particular.

Immunochemical characterization of glutamine synthetase from Neurospora crassa glutamine auxotrophs

Glutamine synthetase derived from two Neurospora crassa glutamine auxotrophs was characterized. Previous genetic studies indicated that the mutations responsible for the glutamine auxotrophy are allelic and map in chromosome V. When measured in crude extracts, both mutant strains had lower glutamine synthetase specific activity than that found in the wild-type strain. The enzyme from both auxotrophs and the wild-type strain was partially purified from cultures grown on glutamine as the sole nitrogen source, and immunochemical studies were performed in crude extracts and purified fractions. Quantitative rocket immunoelectrophoresis indicated that the activity per enzyme molecule is lower in the mutants than in the wild-type strain; immunoelectrophoresis and immunochemical titration of enzyme activity demonstrated structural differences between the enzymes from both auxotrophs. On the other hand, the monomer of glutamine synthetase of both mutants was found to be of a molecular weight similar to that of the wild-type strain. These data indicate that the mutations are located in the structural gene of N. crassa glutamine synthetase.

[Congestive myocardiopathy and early dyastolic closure of the tricuspid valve. Report of a case with acute tricuspidization]

A case with congestive cardiomiopathy and early diastolic closure of the tricuspid valve is presented. This abnormal echocardiographic finding was probably the result of severe tricuspid regurgitation occurring in a restricted right ventricle. The absence of paradoxical septum was determinedly the left ventricular pathology. In this case, echocardiography was more sensitive for the detection of the left sided abnormalities, than the heart cath data.

Nitrogen source regulates glutamine synthetase mRNA levels in Neurospora crassa

Neurospora crassa glutamine synthetase mRNA was measured by its capacity to direct the synthesis of the specific protein in a cell-free system derived from rabbit reticulocytes. N. crassa cultures grown on glutamate as the sole nitrogen source had higher mRNA activities than did those grown on glutamine. The differences were about 10-fold when polysomal RNA was used for translation and about 5-fold when either total cellular RNA or polyadenylic acid-enriched cellular RNA was used. These data indicate that in exponentially growing N. crassa, the nitrogen source regulates glutamine synthetase by adjusting specific mRNA levels.

Genetics and physiology of Neurospora crassa glutamine auxotrophs

This work reports on the isolation and characterization of two glutamine auxotrophs in Neurospora crassa. The mutations responsible for the glutamine-requiring phenotype were very closely linked, and one of them proved to be recessive to wild type. The mutations impaired the conversion of glutamic acid to glutamine and resulted in changes of both the activity and oligomeric structure of the enzyme glutamine synthetase.

Nitrogen regulation of glutamine synthetase in Neurospora crassa

A higher activity of glutamine synthetase (EC 6.3.1.2) was found in Neurospora crassa when NH4+ was limiting as nitrogen source than when glutamate was limiting. When glutamate, glutamine or NH4+ were in excess, a lower activity was found. Immunological titration and sucrose gradient sedimentation of the enzyme established that under all these conditions enzyme activity corresponded to enzyme concentration and that the octamer was the predominant oligomeric form. When N. crassa was shifted from nitrogen-limiting substrates to excess product as nitrogen source, the concentration of glutamine synthetase was adjusted with kinetics that closely followed dilution by growth. When grown on limiting amounts of glutamate, a lower oligomer was present in addition to the octameric form of the enzyme. When the culture was shifted to excess NH4+, glutamine accululated at a high rate; nevertheless, there was only a slow decrease in enzyme activity and no modification of the oligomeric pattern.

Neurospora crassa glutamine synthetase. Role of enzyme synthesis and degradation on the regulation of enzyme concentration during exponential growth

The specific activity of Neurospora crassa glutamine synthetase varies according to the nitrogen source in which the organism is grown. In a poor nitrogen source such as glutamate, the specific activity of the enzyme is higher than that found in good nitrogen sources such as ammonium or glutamine. These differences in specific enzyme activity correspond to differences in enzyme concentration. The relative rates of glutamine synthetase synthesis and degradation were measured in exponential cultures grown in different nitrogen sources. The differences in enzyme concentration are explained by differences in the relative rate of enzyme synthesis.

Neurospora crassa glutamine synthetase. Translation of specific messenger ribonucleic acid in a cell-free system derived from rabbit reticulocytes

The total reticulocyte lysate cell-free protein-synthesizing system was incubated in the presence of Neurospora crassa RNA. With the aid of an antibody directed against purified N. crassa glutamine synthetase, the synthesis of a specific protein was detected. This protein precipitates with antiglutamine synthetase using both direct and indirect procedures, migrates with the same molecular weight as the monomer of N. crassa glutamine synthetase when subjected to acrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, and chromatographs as N. crassa glutamine synthetase on anthranilate-bound Sepharose. These data indicate the translation of the mRNA that codes for N. crassa glutamine synthetase. This RNA behaves as poly(A)-containing material when fractionated on oly(U)-Sepha-rose.

Neurospora crassa glutamine synthetase. Purification by affinity chromatography and characterization of subunit structure

Neurospora crassa glutamine synthetase was purified to homogeneity by a procedure based on affinity chromatography. The enzyme is adsorbed to a matrix of anthranilic acid bound to Sepharose and eluted with AMP. Different experimental approaches indicate that the enzyme has an octameric structure formed by subunits of identical molecular weight.

Ovalbumin mRNA, complementary DNA and hormone regulation in chick oviduct

Chick oviduct differentiation is controlled by various steroid hormones, including both oestrogen and progesterone. Administration of oestrogen to chicks results in differentiation of tubular gland cells, which synthesize differentiated cell products, including ovalbumin and conalbumin. Ovalbumin can constitute as much as 60% of the protein synthesized by oviduct in the fully stimulated chick. Methods have been developed that allow for the quantitative assay of ovalbumin mRNA, the specific isolation of ovalbumin synthesizing polysomes by use of immunologic techniques, as well as the synthesis of a DNA probe complementary to the ovalbumin mRNA. With these techniques we have found that the rate of ovalbumin synthesis is proportional to the content of ovalbumin mRNA. Hybridization studies using the DNA probe indicate that there are only two copies of the ovalbumin gene per genome, and that there is no amplification of the ovalbumin genes to account for the large amount of ovalbumin synthesized.

Studies on the advent of ureotelism. The effects of bivalent cations on the capacity of the hepatic arginase of the Mexican axolotl to hydrolyse endogenous arginine

1. The effects of 19 bivalent cations on the activity, stability and capacity to hydrolyse endogenous arginine of axolotl liver arginase were studied. 2. It was found that Fe(2+), Co(2+), Ni(2+) and Zn(2+), as well as Mn(2+), stabilize the enzyme and render it able to hydrolyse endogenous arginine. 3. By using different concentrations of Co(2+) and Ni(2+) it was possible to dissociate the effect of each of the metal ions on the activity and stability of arginase from that on its capacity to hydrolyse endogenous arginine. 4. The effects of Mn(2+), Co(2+) and Ni(2+) on the activity and stability of arginase in the homogenate were also observed with purer preparations of the enzyme. 5. It is suggested that the capacity to hydrolyse endogenous arginine is a consequence of the integration of arginase with the arginine-formation sites.

Studies on the advent of ureotelism. Factors that render the hepatic arginase of the Mexican axolotl able to hydrolyse endogenous arginine

1. A study was undertaken of the conditions that might operate in the synthesis and hydrolysis of arginine by axolotl liver homogenate to test a previous postulate that liver arginase of the non-metamorphosed Mexican axolotl is not able to hydrolyse arginine formed from citrulline and aspartic acid, though it can split exogenous arginine, and also that an enhanced capacity to hydrolyse endogenous arginine plays a major role in the advent of ureotelism observed during the metamorphosis of the axolotl. 2. It was found that the arginase from axolotl liver is very unstable under the conditions followed, contrary to what is observed in rat liver. 3. Axolotl arginase is able to hydrolyse endogenous arginine if preserved. 4. Mn(2+) protects the enzyme and renders it able to split endogenous arginine. 5. It is suggested that the metal ion produces a change of conformation of the enzyme that, being stable, is capable of hydrolysing the amino acid, or that the new conformation is appropriate for interaction with the sites of arginine synthesis.