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Biomedical subjects

G Kramer

Publications and source records attributed to G Kramer.

At least 73 records · Page 4Linked to original sources
PubMed1995

Elongation and folding of nascent ricin chains as peptidyl-tRNA on ribosomes: the effect of amino acid deletions on these processes.

Ricin A-chain was used as a test protein to study the effects of deletion of codons on the ribosomal synthesis, release and chaperone-mediated folding of the proteins. Synthesis of wild-type ricin and five mutant proteins was carried out in an Escherichia coli cell-free coupled transcription/translation system from otherwise identical non-linearized plasmids. The deletions involved small numbers of contiguous amino acid residues at different points from the N terminus to the C terminus of the wild-type protein. Deletion of the N-terminal 20 amino acid residues caused a 45% reduction in total protein synthesis whereas deletion of the next three amino acid residues caused a 1.5-fold increase in synthesis compared with wild-type with an accumulation of full-length polypeptides as peptidyl-tRNA in the ribosomal P site. Intermediate levels of synthesis and release were seen with the other three mutants. Enzymatic activity was detected only with wild-type protein and a mutant lacking the C-terminal five amino acid residues. These were the only ricin species in which chaperone-dependent reactions could be detected by fluorescence from coumarin incorporated with methionine at the N terminus of the proteins. By using sparsomycin to block termination of full-length peptidyl-tRNA, it was demonstrated that the chaperone-mediated reactions detected by fluorescence occur on the ribosomes and involve folding of the nascent protein as peptidyl-tRNA. The results presented provide a direct demonstration of two points of fundamental importance: folding of nascent proteins involving chaperone-mediated reactions can occur on ribosomes and is directly related to the conformation of the native enzyme. Deletion of amino acid residues at different points from the N terminus to the C terminus affects the reactions of elongation, chaperone-mediated folding and release of full-length protein.

Cell-Free System↗
PubMed1995

The importance of the N-terminal segment for DnaJ-mediated folding of rhodanese while bound to ribosomes as peptidyl-tRNA.

Two lines of evidence indicate the importance of the N-terminal portion of rhodanese for correct folding of the nascent ribosome-bound polypeptide. A mutant gene lacking the codons for amino acids 1-23 of the wild-type protein is expressed very efficiently by coupled transcription/translation on Escherichia coli ribosomes; however, the mutant protein that is released from the ribosomes is enzymatically inactive. The mutant protein does not undergo the reaction that is promoted by the bacterial chaperone, DnaJ, which appears to be essential for folding of ribosome-bound rhodanese into the native conformation. The effect of DnaJ is monitored by fluorescence from coumarin cotranslationally incorporated at the N terminus of nascent rhodanese. Secondly, a synthetic peptide corresponding to the N-terminal 17 amino acids of the wild-type protein interferes with the synthesis of wild-type rhodanese but has much less effect on the synthesis of the N-terminal deletion mutant. The N-terminal peptide inhibits the effect of DnaJ on the nascent wild-type rhodanese and blocks the chaperone-mediated release and activation of ribosome-bound full-length rhodanese polypeptides that accumulate during in vitro synthesis. The results lead to the hypothesis that the N-terminal segment of rhodanese is required for its chaperone-dependent folding on the ribosome.

Escherichia coli Proteins↗
PubMed1995

Inhibition of the release factor-dependent termination reaction on ribosomes by DnaJ and the N-terminal peptide of rhodanese.

A peptide consisting of the 17 N-terminal amino acids of native bovine rhodanese in combination with the chaperone DnaJ specifically inhibits release factor- and stop codon-dependent hydrolysis of N-formylmethionine from N(formyl)-methionyl-tRNA bound with AUG to salt-washed ribosomes. Neither the peptide nor DnaJ by itself causes this inhibition. The N-terminal peptide and DnaJ both singularly and combined do not affect the peptidyltransferase reaction per se. The total amount of rhodanese synthesized in the cell-free coupled transcription-translation system is reduced by the peptide, with concomitant accumulation of full-length enzymatically inactive rhodanese polypeptides on ribosomes. In combination with DnaJ, the N-terminal polypeptide inhibits the termination and release of full-length rhodanese peptides that have accumulated on Escherichia coli ribosomes during the course of uninhibited coupled transcription-translation in the cell-free system. This inhibition appears to involve release factor 2-mediated termination at the UGA termination codon in the coding sequence for rhodanese. It is suggested that the N-terminal peptide inhibits the binding of the release factor to ribosomes. These data appear to provide the first report of differential inhibition of the termination reaction on ribosomes without inhibition of the peptidyltransferase reaction and peptide elongation.

Amino Acid Sequence↗
PubMed1995

Low plasma homovanillic acid levels in recently abstinent alcoholic men.

OBJECTIVE: To explore dopaminergic mechanisms in alcohol dependence, the authors measured plasma homovanillic acid (HVA) in recently detoxified alcohol-dependent men. METHOD: Plasma HVA was measured in 83 male patients with a diagnosis of alcohol dependence who had maintained documented abstinence for at least 3 weeks and in 69 healthy male comparison subjects. RESULTS: The alcoholic patients as a group had significantly lower levels of plasma HVA than the comparison subjects. This difference was not influenced by any other measured covariate, including a family history of alcohol dependence. CONCLUSIONS: These results imply that factors such as alcohol dependence should be taken into account in future studies of plasma HVA.

Alcohol Drinking↗
PubMed1995

High expression of a CD38-like molecule in normal prostatic epithelium and its differential loss in benign and malignant disease.

PURPOSE: We characterize an undescribed antigen on prostatic epithelial cells, which is recognized by anti-CD38. MATERIALS AND METHODS: Normal (3 cases), benign hyperplastic (10) and carcinomatous (10) prostatic tissues were analyzed using immunohistochemistry, immuno-electron microscopy and the Western blot test. RESULTS: Comparison of prostatic and lymphatic CD38 antigen revealed identical bands at 45 kD. Electron microscopy demonstrated anti-CD38 reactivity on the cytoplasmic membrane and within the secretory vacuoles. Double labeling with anti-cytokeratin types 5/15 and 8/18 confirmed that basal and secretory normal prostatic epithelial cells express CD38. By contrast, a complete loss was found in malignant (52.8%), tumor-surrounding nonmalignant (16.3%) and benign prostatic hyperplasia derived glands (3.7%). CONCLUSIONS: CD38 is a novel prostatic antigen. Its role in intracellular calcium mobilization may contribute to smooth muscle cell contraction and/or sperm motility.

ADP-ribosyl Cyclase↗
PubMed1995

Effects of electroconvulsive therapy on plasma GABA.

There are no published data on the effects of seizures on indices of gamma-aminobutyric acid (GABA) function in human subjects. In study 1, the effects of electroconvulsive therapy (ECT) on free plasma GABA were studied in 39 inpatients with major depressive disorder. Acutely after ECT, free plasma GABA was significantly reduced for up to 1 h after seizure termination, and this finding replicated strongly in a subgroup of six patients who received a second course of ECT. In a second study at a different site that compared sham ECT and real ECT in seven patients, some doubt was raised about the replicability of the acute effect of ECT on GABA levels. Nonetheless, the strength of the findings in the larger study 1 sample suggests that, unlike virtually all other biochemical indices, free plasma GABA may be reduced acutely after ECT. This acute decrease could reflect decreased levels of GABA in brain extracellular space or decreased brain turnover. In study 1, compared with ECT nonresponders, ECT responders had higher GABA levels at both baseline and after a course of ECT. Because plasma GABA levels are known to be low in a subset of patients with major depression, the higher GABA levels observed in clinical responders before and after the ECT course indirectly suggest that patients least abnormal in GABA levels may show superior clinical response. This also suggests that low plasma GABA is not a state marker for depression.

Adult↗
PubMed1994

Chaperone-dependent folding and activation of ribosome-bound nascent rhodanese. Analysis by fluorescence.

Fluorescently labeled rhodanese was synthesized by coupled transcription/translation in a cell-free Escherichia coli system. A derivative of coumarin was co-translationally incorporated at the N terminus of the polypeptide. Molecules released from the ribosomes during the incubation are enzymatically active; however, continued incubation results in accumulation of enzymatically inactive full-length rhodanese polypeptides on the ribosomes. These can be activated and released in the presence of the added chaperones, DnaJ, DnaK, GrpE, GroEL, GroES and ATP. Fluorescence parameters (quantum yield, anisotropy and the emission maximum) of ribosome-bound coumarin-labeled rhodanese are affected differentially by addition of the chaperones individually or sequentially. Rhodanese released from the ribosomes in the presence of all chaperones (enzymatically active) differs in fluorescence properties from rhodanese released by GroES or DnaK only or by puromycin (enzymatically inactive) indicating a difference in conformation. Using sparsomycin, an inhibitor of the peptidyl transferase reaction, full-length rhodanese can be trapped on the ribosomes. A ribosome-bound intermediate formed by DnaJ or DnaJ plus DnaK was demonstrated by the effect of these chaperones on fluorescence spectra resulting from binding of anticoumarin antibodies to the N terminus of newly synthesized rhodanese. The results support the hypothesis that folding of nascent proteins can take place on the ribosome.

Chaperonins↗
PubMed1994

Activation and release of enzymatically inactive, full-length rhodanese that is bound to ribosomes as peptidyl-tRNA.

Synthesis of rhodanese in a cell-free coupled transcription/translation system derived from Escherichia coli leads to an accumulation of full-length rhodanese protein on the ribosomes as well as to enzymatically active protein that is released from the ribosomes into the supernatant fraction. The ribosome-bound protein is enzymatically inactive but can be activated and released from the ribosomes without additional protein synthesis by subsequent incubation in the presence of the added chaperones DnaJ, DnaK, GrpE, GroEL, and GroES plus ATP. Efficient activation requires that all of the chaperones are present together during incubation which yields fully active rhodanese. Incubation in the presence of DnaJ only inhibits release whereas incubation with only GroES or DnaK promotes the release of enzymatically inactive protein. Incubation of the ribosome with puromycin leads to the release of enzymatically inactive protein whereas release and activation in the presence of all of the chaperones is blocked by sparsomycin. The effect of these antibiotics provides very strong evidence that enzymatically inactive, full-length rhodanese is bound to the ribosomes as peptidyl-tRNA and that the peptidyl transferase reaction is required for its release. Considered together, the data indicate that chaperone-mediated late stages of rhodanese folding into the enzymatically active, native conformation are intimately associated with the process of termination and release that occurs as part of the reaction cycle of protein synthesis.

Animals↗
PubMed1994

Learned helplessness sensitizes hippocampal norepinephrine to mild restress.

A proportion of rats exposed to inescapable tailshock stress displayed a performance deficit, termed learned helplessness, in a subsequent shuttlebox avoidance task. The technique of in vivo microdialysis was used to determine hippocampal norepinephrine levels in learned helpless, nonhelpless and nonprestressed control rats. Similar basal norepinephrine levels were detected in samples between rat groups. Following an exposure to a milder form of inescapable shock, an increase in norepinephrine output was detected in learned helpless rats, which was significantly greater than nonhelpless, nonprestressed, or control animals. Thus, inescapable stress appears to sensitize the hippocampus to increase norepinephrine release in response to a subsequent smaller stressor. This hypersensitivity might underlie the avoidance impairment of learned helplessness. Therefore, the possibility exists that similar neurochemical changes may also be responsible for some of the symptoms of human posttraumatic stress disorder (PTSD), such as the poor coping associated with seemingly mild stress.

Animals↗
PubMed1994

Development of a chaperone-deficient system by fractionation of a prokaryotic coupled transcription/translation system.

A coupled transcription/translation system from Escherichia coli has been developed that is very active for protein synthesis but deficient in chaperone proteins. The chaperones GroEL and DnaK distribute during the first ultracentrifugation of the E. coli extract partially with the ribosomes and partially in a liquid, viscous fraction above the ribosomes. Gel filtration chromatography of this latter fraction separates GroEL and DnaK as high-molecular-weight components from the peak of activity of the factors required for protein synthesis. Thus, a chaperone-deficient transcription/translation system can be reconstituted with salt-washed ribosomes. This chaperone-deficient system was used to study synthesis and folding of bacterial dihydrofolate reductase and of rhodanese, a eukaryotic mitochondrial enzyme. Both enzymes were synthesized from nonlinearized plasmids that had the respective coding sequence under the SP6 promoter. Both enzymes were synthesized in active form and with high specific activity in the chaperone-deficient system. A high proportion, about 20% of newly synthesized dihydrofolate reductase and about 50% of rhodanese, stayed with the ribosomes after coupled transcription/translation. No enzymatic activity was detected in this fraction. Addition of the chaperones GroEL/ES and DnaK resulted in a shift of rhodanese molecules from the ribosomes into the supernatant fraction. Nearly all molecules in the supernatant were enzymatically active.

Bacterial Proteins↗
PubMed1994

In vivo release of catecholamines from xenogeneic chromaffin cell grafts with antidepressive activity.

Previous studies in our laboratory have demonstrated that allografts of adrenal medullary tissue and xenografts of isolated bovine chromaffin cells to the rat frontal cortex can increase antidepressive activity in two separate animal models. Biochemical and pharmacological evidence suggest that the most likely mechanism of these antidepressive effects is via local release of catecholamines into the surrounding cortical parenchyma. The aim of the present study was to directly characterize the antidepressive mechanism of chromaffin cell xenografts by utilizing in vivo microdialysis to measure extracellular catecholamine levels from bovine chromaffin cell and control implanted rat frontal cortex. Following transplantation, only bovine chromaffin cell grafted rats displayed significant increases in antidepressive activity, as assessed by the forced swimming test, compared to rats with grafts of bovine adrenal medullary fibroblasts or nontransplanted rats. In vivo microdialysis results revealed remarkably elevated levels of epinephrine (EPI) and norepinephrine (NE), but not dopamine, in dialysates from bovine chromaffin cell-transplanted frontal cortex. The most likely source of these enhanced EPI and NE levels is the grafted xenogeneic chromaffin cells. The results of this study directly demonstrate that xenografts of bovine chromaffin cells to the rat frontal cortex provide a releasable pool of catecholamines for antidepressive activity.

Animals↗
PubMed1994

Does learned helplessness induction by haloperidol involve serotonin mediation?

Learned helplessness (LH) is a behavioral depression following inescapable stress. Helpless behavior was induced in naive rats by the dopamine D2 receptor blocker haloperidol (HDL) in a dose-dependent manner, with the greatest effects seen at 20 mg/kg (IP). Rats were tested 24 h after injection. Haloperidol (IP) increased release of serotonin (5-HT) in medial prefrontal cortex (MPC) as measured by in vivo microdialysis. Perfusion of HDL through the probe in MPC caused increased cortical 5-HT release, as did perfusion of both dopamine and the dopamine agonist apomorphine. Our previous work found that increased 5-HT release in MPC correlates with the development of LH. The present work suggests that increased DA release in MPC, known to occur with both inescapable stress and with HDL, may play a necessary but not sufficient role in the development of LH. Also, this suggests that increased DA activity in MPC leads to increased 5-HT release in MPC and to subsequent behavioral depression.

Animals↗
PubMed1994

In vivo serotonin release and learned helplessness.

Learned helplessness, a behavioral depression caused by exposure to inescapable stress, is considered to be an animal model of human depressive disorder. Like human depression, learned helplessness has been associated with a defect in serotonergic function, but the nature of this relationship is not entirely clear. We have used in vivo microdialysis brain perfusion to measure serotonin (5-hydroxytryptamine, 5HT) in extracellular space of medial frontal cortex in conscious, freely moving rats. Basal 5HT levels in rats perfused before exposure to tail-shock stress did not themselves correlate with subsequent learned helplessness behavior. However, 5HT release after stress showed a significant increase with helpless behavior. These data support the hypothesis that a cortical serotonergic excess is causally related to the development of learned helplessness.

Animals↗
PubMed1994

Serotonin and impulsive/aggressive behavior in cocaine dependent subjects.

1. 10 male cocaine dependent patients and 10 sex matched controls were administered several behavioral measures of aggression including the Buss-Durkee Hostility Inventory, and The Brown-Goodwin Life History of Aggression. 2. All subjects were also administered a buspirone neuroendocrine challenge as a measure of serotonin function. 3. The cocaine dependent subjects were significantly more aggressive than the controls. 4. There was a significant correlation between the growth hormone response to buspirone and behavioral measures of aggression in the cocaine dependent subjects, but not in the controls. 5. There was no difference in the overall growth hormone response between the controls and cocaine dependent subjects, possibly due to differences in metabolism of buspirone. 6. This study supports a role for serotonin in aggression in cocaine dependent subjects.

Adult↗
PubMed1994

Phenotype and function of peripheral and prostatic lymphocytes in patients with benign prostatic hyperplasia.

In a previous report, we demonstrated intense lymphocytic infiltration of all benign prostatic hypertrophy (BPH) tissues analyzed in conjunction with HLA-DR expression on normally MHC-class-II-negative prostate epithelial cells. The composition of these infiltrates (70 to 80% CD3+ T-cells, but no granulocytes) resembles the situation seen in immune responses against altered self or self rather than against foreign antigens (infection). In the present study, phenotypic and functional immunoassays were used in order to investigate whether T-cells in BPH are indeed activated, and whether this activation is systemic or restricted locally to the prostate. Analysis of T-cell activation marker expression and proliferation requirements provided substantial evidence that these infiltrating lymphocytes, in contrast to their peripheral counterparts, are chronically activated. Since local accumulation of activated lymphocytes can cause tissue destruction, high concentrations of cytokines, and consequently tissue rebuilding, this process might contribute to the pathogenesis of BPH.

Adult↗
PubMed1994

A preliminary neuroendocrine study with buspirone in major depression.

We administered the serotonin-1a agonist buspirone (0.4 mg/kg orally) as a neuroendocrine challenge agent to a group of male patients with DSM-III-R major depressive disorder (MDD) (n = 13) and a group of male healthy controls (n = 10). The primary hypothesis of the study was that the prolactin response to buspirone would be blunted in the depressed patients. The prolactin response was significantly lower in depressed patients than in controls. There was no significant relationship between placebo corrected-peak prolactin level and severity of depression or suicidality. There was a nonsignificant trend for the melancholic (n = 5) depressed patients to have a lower placebo corrected-peak prolactin level than nonmelancholic depressed patients (n = 8). Our findings support a role for the serotonin-1a receptor in the etiology of MDD, specifically at the postsynaptic site.

Adult↗