Involvement of glutamate 268 in the active site of human liver mitochondrial (class 2) aldehyde dehydrogenase as probed by site-directed mutagenesis

On the basis of chemical modification studies, it was postulated that glutamate 268 was a component of the active site of liver aldehyde dehydrogenase [Abriola, D. P., Fields, R., MacKerell, A. D., Jr., & Pietruszko, R. (1987) Biochemistry 26, 5679-5684]. To study its role, the residue in human liver mitochondrial (class 2) aldehyde dehydrogenase was mutated to an aspartate, a glutamine, or a lysine, and the enzyme was expressed in Escherichia coli. The mutations did not affect the Km values for NAD or propionaldehyde, but grossly affected the catalytic activity of the enzymes when compared to recombinantly expressed native enzyme; the mutant enzymes had less that 0.4% of the specific activity of the recombinantly expressed native aldehyde dehydrogenase. The mutations also caused a long lag phase to occur prior to the steady state phase of the reaction. The activity of the mutant enzymes could not be restored by the addition of general bases such as sodium acetate, sodium formate, or imidazole. The Kd for NADH was essentially identical for the E268Q mutant and native enzyme. The three mutant forms of the enzyme possessed less than 0.8% of the esterolytic activity of the recombinantly expressed native enzyme. Pre-steady state analysis showed that there was no burst of NADH formation in the dehydrogenase reaction or of p-nitrophenol formation in the esterase reaction. This can be interpreted as implying that glutamate 268 may function as a general base necessary for the initial activation of the essential cysteine residue (302), rather than being involved in only the deacylation or hydride transfer step.(ABSTRACT TRUNCATED AT 250 WORDS)

Site directed mutagenesis to probe for active site components of liver mitochondrial aldehyde dehydrogenase

Mutational analysis allowed us to rule out an essential role for the histidine residues and for serine 74 in mammalian aldehyde dehydrogenase. The later though, was found to be important in coenzyme interaction. The function of the serine could not be replaced by threonine or by cysteine. The absolute requirement for cysteine 302 and for glutamate 268 was verified using mutational analysis. The fact that these two residues are completed conserved among all aldehyde dehydrogenases is consistent with their being essential in the catalytic process.

Evaluation of electrostatic and hydrophobic effects on the interaction of mitochondrial signal sequences with phospholipid bilayers

The information that directs a nuclear-coded protein to be imported into mitochondria resides in an N-terminal extension, called a signal sequence. The primary sequences of all known ones differ. The only common feature is their ability to theoretically form an amphiphilic, positively charged, alpha-helix. We previously showed that a short stable helical segment was required for a peptide to be functional in import [Wang, Y., & Weiner, H. (1993) J. Biol. Chem. 268, 4759-4765]. Here we investigate the interaction of three altered signal sequences with phospholipid membranes containing cardiolipin to ascertain the importance of electrostatic and hydrophobic interactions with the membrane. The three already described peptides were derivatives of the signal sequence from aldehyde dehydrogenase, which is composed of three segments, two helices separated by a linker. ANCN had the C-helix replaced by the N-helix of the signal sequence of cytochrome c oxidase subunit IV, ANCC had the C-terminal helix replaced by the C-terminal random coil of cytochrome oxidase subunit IV, and linker deleted had the linker region deleted. ANCC, which functioned poorly as a signal sequence, had a very low affinity for binding to the negatively charged membranes. In contrast, both ANCN and linker deleted showed a relatively high affinity for the membranes and were capable of functioning as a good leader sequence. It appears that linker deleted possessed a stronger hydrophobic effect with membranes while ANCN had a higher electrostatic interaction. On the basic of these studies, a model was proposed to describe the interaction of mitochondrial signal sequences with negatively charged phospholipid membranes involving electrostatic interaction for initial binding and hydrophobic interaction for insertion.(ABSTRACT TRUNCATED AT 250 WORDS)

Electroencephalographic coherence in acquired immune deficiency syndrome

We studied a quantitative electroencephalographic (EEG) measure, coherence, in 28 patients with acquired immune deficiency syndrome (AIDS) and 56 uninfected volunteers. Compared with uninfected subjects, AIDS patients had increased coherence in the 6- to 10-Hz band. The largest increases in coherence were between frontal and occipital regions and between temporal and frontal regions. Coherence within contiguous regions was less affected. Eight of the 28 AIDS patients (29%) had clinically abnormal EEG findings, compared with four of the 56 uninfected control subjects (7%). Among the AIDS patients, 12 had normal neuropsychological performance, nine had mild impairment, and six had moderate impairment. Coherence was increased in each subgroup of AIDS patients, including those with normal neuropsychologic performance and/or normal clinical EEG results. AIDS patients were then classified by quantitative EEG power in frontal head regions as "abnormal" (the upper third of patients) or "normal" (the remainder). Increased coherence was found among both groups. Because the development of abnormal neuropsychological performance or a clinically abnormal EEG examination indicates relatively advanced central nervous system disease, alterations in specific coherence measures may detect subclinical effects of the human immunodeficiency virus on brain function before other changes are evident.

Involvement of serine 74 in the enzyme-coenzyme interaction of rat liver mitochondrial aldehyde dehydrogenase

It has been suggested that the active site nucleophile in sheep liver aldehyde dehydrogenase was not a cysteine residue but was a serine located at position 74 [Loomes, K. M., Midwinter, G. G., Blackwell, L. F., & Buckley, P. D. (1990) Biochemistry 29, 2070-2080]. This enzyme form has not yet been cloned and expressed, but since the rat liver mitochondrial enzyme has been and shares 70% sequence homology with other cytosolic aldehyde dehydrogenases, the residue in the rat enzyme was converted into an alanine to test for the necessity of a hydroxyl group at that position. The recombinantly expressed mutant enzyme possessed 10% catalytic activity, but the Km for NAD increased from 10 to 1900 microM while the Kms for various aldehydes were unchanged. Kinetic analysis revealed that the dissociation constant for NAD also increased in the mutant as did k1, the on velocity for NAD binding. The mutant enzyme bound poorly to an AMP-Sepharose column and did not interact as well with NADH, as determined by fluorescence enhancement binding studies, or with ADP-ribose, a competitive inhibitor. Pulse-chase analysis showed that the mutant was as stable as was the recombinantly expressed native enzyme. It was less stable to heat denaturation at 50 degrees C (half-life of 1 min compared to 4). Converting the alanine to a cysteine or a threonine did not restore native-like properties of the enzyme. These mutants had kinetic properties very similar to those of the alanine mutant.(ABSTRACT TRUNCATED AT 250 WORDS)

Structure of the signal sequences for two mitochondrial matrix proteins that are not proteolytically processed upon import

The N-terminal sequences of rhodanese and 3-oxoacyl-CoA thiolase, two mitochondrial matrix proteins that are not proteolytically processed upon import, have been studied by NMR and CD spectroscopy. In aqueous trifluoroethanol, in the presence of micelles, and in the presence of small unilamellar vesicles (SUVs), these peptides form alpha-helical structures beginning near the N-terminus and extending, continuously, for at least three helical turns. This result is consistent with a previous finding that a mutant rat liver mitochondrial aldehyde dehydrogenase signal sequence we designed, which formed a continuous alpha-helix, could successfully direct protein import but was not proteolytically processed (Thornton, K., Wang, Y., Weiner, H., & Gorenstein, D. G. (1993) J. Biol. Chem. 268, 19906-19914). From these three examples, a model is developed which suggests that a mitochondrial signal sequence that has an N-terminal alpha-helix longer than 11 residues can take on the necessary conformation to be imported but cannot adopt the necessary conformation to be processed.

Repeated bereavement, depressed mood, and immune parameters in HIV seropositive and seronegative gay men

The relationships among bereavement, depressed mood, and immunologic patterns prognostic for the development of acquired immunodeficiency syndrome (AIDS) were determined in a sample of human immunodeficiency virus (HIV) seropositive gay men and a comparison group of HIV seronegative gay men. Immunologic parameters were assessed in 45 men who had recently experienced the deaths of close friends and 45 matched nonbereaved men. No immune differences were found between bereaved and nonbereaved men. Among the HIV seropositive nonbereaved men, higher depressed mood was significantly associated with fewer CD4 (helper/inducer) T lymphocytes, more activated CD8 (suppressor/cytotoxic) T cells, and lower proliferative responses to the mitogen phytohemagglutinin. In summary, HIV seropositive men who reported higher levels of depressed mood not associated with bereavement demonstrated immunologic patterns consistent with HIV activity and progression.

Effects of changing glutamate 487 to lysine in rat and human liver mitochondrial aldehyde dehydrogenase. A model to study human (Oriental type) class 2 aldehyde dehydrogenase

Many Oriental people possess a liver mitochondrial aldehyde dehydrogenase where glutamate at position 487 has been replaced by a lysine, and they have very low levels of mitochondrial aldehyde dehydrogenase activity. To investigate the cause of the lack of activity of this aldehyde dehydrogenase, we mutated residue 487 of rat and human liver mitochondrial aldehyde dehydrogenase to a lysine and expressed the mutant and native enzyme forms in Escherichia coli. Both rat and human recombinant aldehyde dehydrogenases showed the same molecular and kinetic properties as the enzyme isolated from liver mitochondria. The E487K mutants were found to be active but possessed altered kinetic properties when compared to the glutamate enzyme. The Km for NAD+ at pH 7.4 increased more than 150-fold, whereas kcat decreased 2-10-fold with respect to the recombinant native enzymes. Detailed steady-state kinetic analysis showed that the binding of NAD+ to the mutant enzyme was impaired, and it could be calculated that this resulted in a decreased nucleophilicity of the active site cysteine residue. The rate-limiting step for the rat E487K mutant was also different from that of the recombinant rat liver aldehyde dehydrogenase in that no pre-steady-state burst of NADH formation was found with the mutant enzyme. Both the rat native enzyme and the E487K mutant oxidized chloroacetaldehyde twice as fast as acetaldehyde, indicating that the rate-limiting step was not hydride transfer or coenzyme dissociation but depended upon nucleophilic attack. Each enzyme form showed a 2-fold activation upon the addition of Mg2+ ions. Substituting a glutamine for the glutamate did not grossly affect the properties of the enzyme. Glutamate 487 may interact directly with the positive nicotinamide ring of NAD+ for the Ki of NADH was the same in the lysine enzyme as it was in the glutamate form. Because of the altered NAD+ binding properties and kcat of the E487K variant, it is assumed that people possessing this form will not have a functional mitochondrial aldehyde dehydrogenase.

A repressive coping style protecting from emotional distress in low-renin essential hypertensives

OBJECTIVE

To investigate the relationship between the behavioural characteristics and specified subgroups of patients with essential hypertension.

DESIGN AND METHODS

Fifty-four patients were classified into groups with a high (n = 9), normal (n = 35) or low plasma renin activity (n = 10), and were compared with 20 normotensive subjects by psychological tests. Standardized tests were used to measure anger expression, defensiveness and the subjects' psychological status (e.g. anxiety, depression).

RESULTS

A repressive coping style, defined by a high defensiveness and low anxiety levels, was found significantly more often in patients with low than in patients with high plasma renin activity and normotensive subjects. The patients with high plasma renin activity scored significantly higher on suppressed anger, anxiety and interpersonal sensitivity than did those with low plasma renin activity. The scores of the normal plasma renin activity group were similar to those of the normotensive group.

CONCLUSIONS

The results underline that there is not one hypertensive 'personality'. Whereas the patients with a high plasma renin activity appear to be more susceptible to emotional conflicts, the patients with low plasma renin activity report low emotional distress and maintain an apparently well-adjusted facade.

[Is the "biopsychosocial model" a helpful construct?]

In 1977, G. L. Engel proposed a biopsychosocial model, applicable to all illness and disease. It was based on systems theory which orders the world into a ladder (of systems) from the most elementary particles to social phenomena and the cosmos. Systems theory was proposed to combat reductionism and to deal with complexity and order. Central to that theory is the concept of emergence that the properties of each "higher" or more complex system are not explainable either by their components nor by those at a lower level. However, no one form of complexity exists. Some forms of complexity arise out of the interactions of the components, especially as the result of feed-back, which in turn allows us to understand order, and sudden change. Living systems are characterized by genetic programs, self-replication, self-organization and adaptability. These properties exist at every "level", and thus make systems theory and its hierarchies no longer necessary, and also eliminate the concept of emergence.

Repeated bereavement, depressed mood, and immune parameters in HIV seropositive and seronegative gay men

The relationships among bereavement, depressed mood, and immunologic patterns prognostic for the development of acquired immunodeficiency syndrome (AIDS) were determined in a sample of human immunodeficiency virus (HIV) seropositive gay men and a comparison group of HIV seronegative gay men. Immunologic parameters were assessed in 45 men who had recently experienced the deaths of close friends and 45 matched nonbereaved men. No immune differences were found between bereaved and nonbereaved men. Among the HIV seropositive nonbereaved men, higher depressed mood was significantly associated with fewer CD4 (helper/inducer) T lymphocytes, more activated CD8 (suppressor/cytotoxic) T cells, and lower proliferative responses to the mitogen phytohemagglutinin. In summary, HIV seropositive men who reported higher levels of depressed mood not associated with bereavement demonstrated immunologic patterns consistent with HIV activity and progression.

Quantitative EEG in patients with AIDS and asymptomatic HIV infection

Although neuropsychiatric abnormalities are common in subjects with the acquired immunodeficiency syndrome (AIDS), they are less frequent in asymptomatic human immunodeficiency virus (HIV) seropositive subjects. In contrast, others have reported high rates of electroencephalographic (EEG) abnormality among asymptomatic subjects. Here we report clinical and quantitative EEG findings across all stages of the disease in order to define when during the course of illness abnormalities are detectable. We studied 28 men with AIDS, 32 men with asymptomatic HIV infection, and 56 uninfected controls using clinical and quantitative EEG, measures of immunosuppression, and tests of neuropsychological performance. All were gay or bisexual without other significant risk factors for encephalopathy. We found very low rates of clinical EEG abnormality (less than 7%) among the asymptomatic HIV-infected group, a rate comparable to those of the uninfected group (7.1%). There were no differences between asymptomatic HIV-seropositive subjects and uninfected controls on quantitative EEG measures. Among AIDS patients 28.6% had abnormal clinical electroencephalograms. On quantitative measures, the greatest differences were found in the 6-10 Hz band, where AIDS patients had consistently increased absolute power, relative power, and coherence compared to the uninfected and asymptomatic seropositive groups. A subgroup (n = 9) of asymptomatic HIV-seropositive subjects had worsening performance on Trailmaking test, part B, at or after the time of recording. This subgroup had quantitative electroencephalographic measures similar to those of the AIDS patients and different from the remainder of the asymptomatic HIV-seropositive group.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional differences in brain electrical activity in dementia: use of spectral power and spectral ratio measures

The pathologic changes in dementia of the Alzheimer's type (DAT) commonly affect selected brain regions. The cortical areas affected in multi-infarct dementia (MID) are less predictable and may be secondary to subcortical gray or white matter damage that is widespread in MID. We compared several types of quantitative EEG power measures (absolute and relative power, and ratios of power) to determine their regional distribution, and their association with changes in cognitive status and age. We examined 49 subjects with clinically diagnosed mild-to-moderate DAT, 29 with mild-to-moderate MID, and 38 elderly controls (CON). We used discriminant analysis to identify, for each parameter type, the brain region and frequency band where the parameter best distinguished between groups of subjects. The parameters showed regional differences in distinguishing between DAT and MID subjects, and in their association with age and cognitive status. All parameters were useful for detecting differences between normal and demented subjects and correctly identified comparable proportions of subjects as having dementia. Subjects who were abnormal on several parameters were much more likely to have dementia. The additive effects of these parameters in correct classification suggest that they may be monitoring different physiologic processes. Combinations of several types of parameters may be more useful than individual parameters for distinguishing demented from non-demented subjects.

Sucrose-phosphate synthase phosphatase, a type 2A protein phosphatase, changes its sensitivity towards inhibition by inorganic phosphate in spinach leaves

The activity of a type 2A protein phosphatase from spinach leaves was monitored using phosphorylated sucrose-phosphate synthase (SPS) as a substrate. After partial purification the overall activities of sucrose-phosphate synthase phosphatase (SPS-P) recovered from leaves harvested in the dark and in the light did not vary. However, SPS-P preparations from darkened leaves were more strongly inhibited by inorganic phosphate and certain phosphorylated compounds than preparations from illuminated or mannose fed leaves. We conclude, that activation of SPS involves an interconversion of multiple forms of SPS-P activity.

Import, processing, and two-dimensional NMR structure of a linker-deleted signal peptide of rat liver mitochondrial aldehyde dehydrogenase

Previous NMR studies (Karslake, C., Piotto, M. E., Pak, Y. M., Weiner, H., and Gorenstein, D. G. (1990) Biochemistry 29, 9872-9878) had shown that a 22-amino acid signal peptide of rat liver aldehyde dehydrogenase (ALDH) when bound to a micelle had two amphiphilic alpha-helices, one located at the N terminus and the other at the C terminus. It was shown that deletion of either helix caused the precursor protein not to be imported (Wang, Y., and Weiner, H., (1993) J. Biol. Chem. 268, 4759-4765). The two helices are separated by a Arg-Gly-Pro flexible "linker" region, and to test the role of this linker region in the import and processing of the precursor protein, we deleted it from the ALDH signal peptide and precursor protein. The 19-amino acid signal peptide of ALDH, to which has been added 3 residues at the C terminus and from which has been deleted the 3-residue flexible linker region, has been studied by two-dimensional NMR in a dodecylphosphocholine micelle. In this membrane-like environment the peptide contains a single alpha-helical segment that extends almost the entire length of the peptide. NH exchange experiments show residues on the hydrophobic face of the peptide to exchange much more slowly than those of the hydrophilic face. Combined with the previous study, these results suggest that precursor protein import simply requires a sufficiently long amphiphilic helix (or helices) to bind stably to the membrane. The N and C helices of native ALDH are only about 6-8 residues long; this represents only about two turns of a helix, and either helix on its own does not provide enough stabilization to ensure folding and binding to the membrane. The linker-deleted ALDH peptide contains a single helix of 12-14 residues that is long enough to provide a hydrophobic surface that can stably interact with the hydrophobic interior of the membrane. The function of the C helix in the native signal peptide is therefore to enhance the stability and binding of the N-terminal signal to the membrane. Significantly, unlike native ALDH precursor protein, the linker-deleted signal peptide precursor protein could no longer be processed after import into mitochondria. As explained by modeling of the alpha-helix and the NH exchange rate data, the precursor protein requires that the first several residues of the mature protein be part of the hydrophobic membrane associated face of the helix.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of the highly conserved histidine residues in rat liver mitochondrial aldehyde dehydrogenase as studied by site-directed mutagenesis

One histidine residue (H235) is conserved in all known aldehyde dehydrogenases (ALDH), from Escherichia coli to human, except for those from P. oleovorans and rat hepatoma. Kinetic studies with horse liver mitochondrial ALDH indicated that a group with a pKa of 7 may be involved in the active site. Using site-directed mutagenesis, the four conserved histidine residues of the six histidines in rat liver mitochondrial ALDH were converted to alanines. Only modification of H235 and H29 caused alterations in properties of the enzyme. H29A had a decreased pI suggesting that this residue may normally be protonated. Its Vmax increased, as did the Km for NAD+, while the Km for propionaldehyde decreased. H235A had the same pI as the native enzyme but the Vmax decreased by 50%. Like native enzyme, H235A was active in Hepes and Mops buffer as well as in phosphate buffer. Purified H235A was thermally less stable than was native enzyme. H235 was also changed to F, Y, E, K, and Q. All of these substitutions resulted in the formation of insoluble aggregates or inclusion bodies when they were expressed in E. coli. It appears then that the highly conserved histidine residues may not be functioning as a general base in the deacylation step as we originally suggested. Instead, both H29 and H235 may be of structural importance and the presence of a histidine residue at position 235 may be required for the newly synthesized peptide to fold and/or assemble into the native conformation of ALDH.

Cloning and expression of the full-length cDNAS encoding human liver class 1 and class 2 aldehyde dehydrogenase

The amino acid sequences of both human class 1 and 2 aldehyde dehydrogenase (ALDH) and the sequences of the genes coding for them are known. Based on this sequence data, we designed primers and isolated the full-length cDNAs encoding both isozymes from a human liver mRNA pool. cDNAs were subcloned in the plasmid pT7-7 and expressed in Escherichia coli with a yield of approximately 3 mg ALDH protein/liter of cell culture, although only one-third of the enzyme was soluble. The soluble recombinantly expressed ALDHs were purified to homogeneity using a hydroxyacetophenone-Sepharose affinity column. The mitochondrial isozyme had a subunit molecular weight of 55 kDa, an isoelectric point of 4.9, and a specific activity of 1.10 units/mg, which were in good agreement with that from the native enzyme. The expressed cytosolic isozyme had the same subunit molecular weight (55 kDa) and pI (5.4) as that reported for the native enzyme and had a specific activity of 0.26 units/mg. The expressed mitochondrial isozyme could be recognized by antibodies raised against rat mitochondrial ALDH, whereas the cytosolic isozyme could be recognized by antibody raised against horse cytosolic ALDH.

Serial quantitative EEG among elderly subjects with delirium

Serial quantitative electroencephalographic (QEEG) studies were performed in 33 elderly delirious, demented, and control subjects to determine which QEEG variables were associated with changes in clinical state as measured by the Folstein Mini-mental State Examination (MMSE). Conventional EEGs and brain maps were independently rated by two electroencephalographers without knowledge of clinical diagnoses. Correlational analyses were performed using these ratings, along with numerical data from QEEG. In the delirium group (n = 15), changes in scores for the relative power map and changes in relative power in the alpha band had significant associations with changes in MMSE. In the dementia group (n = 10), changes in score for absolute power maps and changes in absolute power in the delta band had significant associations with changes in MMSE. In the control group, changes in MMSE over time were negligible. These findings have potential clinical utility in diagnosing delirium, and in providing a quantitative measure of its severity, which can be used serially.

T cell responses to myelin basic protein in experimental autoimmune encephalomyelitis-resistant BALB/c mice

In strains of mice that are susceptible to experimental autoimmune encephalomyelitis (EAE), cloned CD4+ T cells reactive with autologous myelin basic protein (MBP) have been shown to cause disease when transferred to naive syngeneic recipients. Recent reports indicate that under particular experimental conditions, 'resistant' strains of mice can also develop EAE, although cloned cells have not been isolated and characterized. An analysis of the characteristics of a panel of MBP-specific T cells and the antigen presenting capability of CNS-derived cells obtained from the resistant strain BALB/c is presented here. The data demonstrate that immunization of EAE-resistant BALB/c mice results in the activation of a heterogeneous group of T cells reactive with autologous MBP. Both peripheral antigen presenting cells, as well as microglia isolated from brains of BALB/c mice, are capable of stimulating these cloned MBP-specific T cells to proliferate. When optimally activated in vitro and then injected in vivo into syngeneic BALB/c recipients, three clones studied induced severe cachexia, resulting in loss of up to 35% of body weight before death. Two of the clones also induced clinical and histological EAE, while the third induced only occasional histological evidence of disease. Differences in epitope recognition, T cell receptor usage, cytokine profiles or regulatory mechanisms of self tolerance, may play important roles in preventing potentially destructive autoimmune reactions by these T cells capable of recognizing autologous myelin in the central nervous system.

Cervical laminectomy and foraminotomy as surgical treatment of cervical spondylosis: a follow-up study with analysis of failures

Ninety patients were followed after undergoing multilevel cervical laminectomy for cervical myeloradiculopathy secondary to cervical stenosis. Follow-up data was obtained by chart review and phone interview for all patients; 20% were examined at follow-up as well; 77% of patients were improved, 13% without change, and 10% worse at follow-up. No patients deteriorated in the immediate postoperative period. Greater than 50% of severely disabled patients had an excellent result, and 78% improved somewhat. It is concluded that cervical laminectomy is an effective procedure for treating patients with cervical spondylosis causing myeloradiculopathy. Reasons for failure of this procedure, although rarely identified on follow-up examination, are reviewed and briefly discussed.

The presequence of rat liver aldehyde dehydrogenase requires the presence of an alpha-helix at its N-terminal region which is stabilized by the helix at its C termini

Previous nuclear magnetic resonance data showed that the conformation of the signal peptide of rat liver mitochondrial aldehyde dehydrogenase in a micelle environment contained a N-helix and a C-helix which were separated by a flexible hinge region (Karslake, C., Piotto, M.E., Pak, Y.K., Weiner, H. and Gorenstein, D. (1990) Biochemistry 29, 9872-9878). Deletion of either helix from the presequence caused complete loss of the precursor import. Switching the positions of the two helices had little effect on import but decreased processing efficiency. Import was not affected by replacing the C-helix with the N-terminal helix of the presequence of cytochrome c oxidase subunit IV, however, it was decreased by replacing the C-helix with the C-terminal random coil of the oxidase's presequence. Circular dichroism studies on the synthesized signal peptides indicated that a helix in the C-segment of aldehyde dehydrogenase signal peptide was needed to stabilize the N-helix. It is concluded that a stable helix in the N-terminal region is necessary for a functional mitochondrial presequence. This helix could be obtained from its own sequence, or from the interaction with other portions of the presequence.

EEG coherence in men with AIDS: association with subcortical metabolic activity

The authors studied the relationship between cerebral metabolism and brain electrical activity in patients with acquired immunodeficiency syndrome (AIDS), using positron-emission tomography and quantitative electroencephalography. Electroencephalographic coherence in the 6-to 10-Hz band correlated positively with thalamic metabolic activity. Coherence adjusted for background activity correlated strongly and positively with basal ganglia metabolic activity. Posterior interhemispheric coherence showed the highest correlations with measures of metabolic activity. These results suggest that changes in coherence may reflect AIDS-related subcortical disease. The high correlations between the two different measures of cerebral activity support the validity of electroencephalographic coherence measures in studies of AIDS-related neuropsychiatric dysfunction.

Purification of liver aldehyde dehydrogenase by p-hydroxyacetophenone-sepharose affinity matrix and the coelution of chloramphenicol acetyl transferase from the same matrix with recombinantly expressed aldehyde dehydrogenase

p-Hydroxyacetophenone was coupled to epoxy-activated Sepharose 6B to generate an affinity chromatographic matrix to purify aldehyde dehydrogenase. Purified beef liver mitochondrial aldehyde dehydrogenase specifically bound to the support and could be eluted with p-hydroxyacetophenone. A post-ammonium sulfate (30-55%) fraction of bovine liver was applied to the affinity gel column and aldehyde dehydrogenase was effectively purified, although not to complete homogeneity, indicating the potential selectivity of the matrix. Both beef liver cytosolic and mitochondrial aldehyde dehydrogenase bound to the column. A post-Cibacron blue Sepharose Cl-6B affinity-fractionated liver mitochondrial aldehyde dehydrogenase was purified to complete homogeneity by p-hydroxyacetophenone-Sepharose, thus eliminating the need for the isoelectric focusing step often employed. p-Hydroxyacetophenone was found to be a competitive inhibitor against propionaldehyde and noncompetitive against NAD. Escherichia coli lysates of recombinantly expressed aldehyde dehydrogenase were purified from E. coli lysates with one major 25-kDa protein contaminant also binding to the column, as detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. The 25-kDa contaminant was found to be chloramphenicol acetyl transferase from sequence analysis and binding studies.

Crystallization and preliminary X-ray investigation of bovine liver mitochondrial aldehyde dehydrogenase

Aldehyde dehydrogenase from bovine liver mitochondria has been crystallized using the sitting drop method of vapor diffusion at 22 degrees C. The crystals formed from solutions containing, 40 mM-sodium citrate, 1 mM-NAD+ and 21% to 24% polyethylene glycol 3400 (pH 5.3 to 5.5). X-ray diffraction data collected from these crystals indicate that the crystals belong to the orthorhombic space group P2(1)2(1)2(1) with cell dimensions of a = 153.7 A, b = 159.37 A and c = 101.45 A. The crystals diffract to at least 2.9 A and a tetramer may comprise the asymmetric unit.

[Psychological factors of non-ulcer dyspepsia]

Given the absence of any demonstrable organic reason for non-ulcer dyspepsia, and the well known fact, that the psyche influences stomach function, it is widely held, that psychological factors cause NUD. To now, studies are concerned with the psychopathology and personality of NUD-patients, their illness behaviour, and with the relation between stress and abdominal pain. A critical review of these studies revealed, that among the psychological variables mainly anxiety and illness behaviour seems to play a central role in NUD. However, future studies should focus more on the distinction towards other functional disorders and on the differentiation within the heterogeneous group of NUD-patients (especially with regard to physiological variables). Besides this, it seems rewarding to examine the so far scientifically neglected group of subjects with abdominal pain, who do not contact a physician.

Identification of factors regulating the phosphorylation status of sucrose-phosphate synthase in vivo

The purpose of this study was to identify the factors that control sucrose-phosphate synthase (SPS)-kinase and SPS-protein phosphatase (SPS-PP) activity in situ, and thereby mediate the activation of SPS by light or mannose. Feeding mannose to excised spinach (Spinacia oleracea) leaves in darkness resulted in a general sequestration of cellular phosphate (as evidenced by accumulation of mannose-6-P and depletion of glucose-6-P [Glc-6-P] and fructose-6-P [Fru-6-P]) and a relatively slow activation of SPS (maximum activation achieved within 90 min). Supplying exogenous inorganic phosphate (Pi) with mannose reduced sequestration of cellular Pi (as evidenced by mannose-6-P accumulation without depletion of hexose-P) and substantially reduced mannose activation of SPS. Thus, depletion of cytoplasmic Pi may be required for SPS activation; accumulation of mannose-6-P alone is clearly not sufficient. It was verified that Glc-6-P, but not mannose-6-P, was an inhibitor of partially purified SPS-kinase, and that Pi was an inhibitor of partially purified SPS-PP. Total extractable activity of SPS-kinase did not vary diurnally, whereas a pronounced light activation of SPS-PP activity was observed. Pretreatment of leaves in the dark with cycloheximide blocked the light activation of SPS-PP (assayed in vitro) and dramatically reduced the rate of SPS activation in situ (in saturating light and carbon dioxide). We conclude that rapid activation of SPS by light involves reduction in cytosolic Pi, an inhibitor of SPS-PP, and light activation of SPS-PP, by a novel mechanism that may involve (directly or indirectly) a protein synthesis step. An increase in cytosolic Glc-6-P, an inhibitor of SPS-kinase, would also favor SPS activation. Thus, the signal transduction pathway mediating the light activation of SPS involves elements of "fine" and "coarse" control.

Inter- and intracellular distribution of amino acids and other metabolites in maize (Zea mays L.) leaves

In illuminated maize (Zea mays L.) leaves, the distribution of triose phosphates, 3-phosphoglycerate, malate and various amino acids between the chloroplastic and the extrachloroplastic compartments of mesophyll and bundle-sheath cells, and the total vacuolar fraction of the leaves, was determined by a combination of previously published methods, for separating mesophyll from bundle-sheath material, and for nonaqueous subcellular fractionation. The results show that the triose phosphate/3-phosphoglycerate ratio in the extrachloroplastic fraction of the mesophyll cells is about 20-fold higher than in the bundle-sheath cells, which is in accordance with a triose phosphate/phosphoglycerate shuttle postulated previously. Whereas the vacuolar compartment was shown to contain most of the cellular malate, amino acids were found to be almost absent from this compartment. The amino-acid pattern in the extrachloroplastic fraction of the bundle-sheath cells largely resembled the pattern in whole leaves. These results show that for future studies the analysis of amino-acid contents in whole maize leaves can be used as a measure for the amino-acid levels in the cytosol of bundle-sheath cells.

Effects of intravenous and oral dexamethasone on selected lymphocyte subpopulations in normal subjects

Our studies describe the effects of 1 mg oral (PO) and intravenous (IV) administration of dexamethasone (DEX) on certain subpopulations of circulating lymphocytes in normal subjects. We compared the outcomes of PO and IV DEX administration because of individual differences in gastro-intestinal absorption of DEX and the issue of noncompliance in patients undergoing the dexamethasone suppression test (DST). Both routes of DEX administration were equally effective in suppressing plasma cortisol levels below 5 micrograms/dl, the customary criterion level. Both routes of DEX administration also significantly decreased the percent and absolute number of CD4+ cells, the CD4+/CD8+ ratio, and the percent and absolute number of virgin, but not of memory, CD4+ cells.

[The organism as a body-mind functional unit--consequences for psychosomatic medicine]

Psychosomatic medicine and research has always been more concerned with a broader and more integrated perspective on health, illness, and disease. It has attempted to study and understand persons in terms of the behaviors of interacting systems--the physiology of the organism. In the past 20 years a language has evolved that speaks of the organism's functions in dynamic, time-related terms. Both phenomenologically and mathematically, functions can be described in terms of rhythmus which, with disease, undergo change. In speaking this new language, some long-standing conceptual issues fade away, and others are clarified. At the same time, these new concepts force the investigator into new ways of designing experiments and analyzing data which may extend and modify them.

Polymorphism of the rat liver mitochondrial aldehyde dehydrogenase cDNA

In humans, a deficiency in mitochondrial aldehyde dehydrogenase (Class 2 ALDH) activity due to a single base-pair exchange in its structural gene serves as a deterrent to excessive alcohol consumption. Differences in Class 2 ALDH isozyme patterns on isoelectric focusing gels have been observed in the selectively bred, alcohol-preferring (P) and alcohol-nonpreferring (NP) lines of rats. To determine whether the differences are the result of sequence variation in the structural gene, we sequenced the cDNAs for Class 2 ALDH from P and NP rats. A synonymous exchange was seen in the codon for amino acid 473 in both lines, when compared with published sequences. Additionally, when the cDNA from P rats was used as reference, a substitution (G for A) was identified in the cDNA of NP rats which changes amino acid 67 from Gln (CAG codon; ALDH2Q allele) to Arg (CGG codon; ALDH2R allele). The Arg for Gln substitution makes the enzyme more basic and could account for the different electrophoretic mobilities. To determine whether the polymorphism was associated with drinking behavior, we genotyped the ALDH2 locus by amplifying rat genomic DNA encompassing the nucleotide exchange followed by probing with allele-specific oligonucleotides. There are highly significant differences in the frequencies of the two alleles in the P and NP rat lines. The frequency of the ALDH2R allele is 63% in the NP line and only 18% in the P line, whereas the frequency of the ALDH2Q allele is 82% in the P line and 37% in the NP line.

Purification and characterization of catalytically active precursor of rat liver mitochondrial aldehyde dehydrogenase expressed in Escherichia coli

The cDNA coding for the precursor (p-ALDH) or mature (m-ALDH) rat liver mitochondrial aldehyde dehydrogenase was cloned in an expression vector pT7-7 and expressed in Escherichia coli strain BL21 (DE3)/plysS. The p-ALDH expressed in E. coli was a soluble tetrameric protein. It exhibited virtually the same specific activity and KmS for substrates as m-ALDH. N-terminal sequencing of isolated p-ALDH provided the evidence that the catalytic activity was not derived from a partially processed mature-like enzyme. The assembly states of both p-ALDH and m-ALDH synthesized in a rabbit reticulocyte lysate were also determined. Both of them were monomers and could not bind to a 5'-AMP-Sepharose column, showing that the monomeric form of the enzyme is inactive. The stabilities in vivo and in vitro were compared between p-ALDH and m-ALDH expressed in E. coli. p-ALDH was less stable than was m-ALDH both in vivo and in vitro. Thus, although the conformations of p-ALDH and m-ALDH are similar, the presence of signal peptide is a destabilizing factor to the p-ALDH. p-ALDH expressed in E. coli could bind to and be translocated into rat liver mitochondria, however, with lower efficiency when compared to the import of p-ALDH synthesized in reticulocyte lysate.

From simplicity to complexity (1950-1990): the case of peptic ulceration--II. Animal studies

Considerable progress has been made in the understanding of the formation of gastric erosions in rats. The role of gastric acid secretion in their pathogenesis has been clarified. Gastric erosions are also associated with slow gastric contractions. With several experimental procedures, the body temperature falls; preventing this decrease averts erosions. A fall in body temperature or exposure to cold is associated with the secretion of thyrotropin-releasing hormone (TRH), and both an increase and decrease in corticotropin-releasing factor (CRF) in discrete regions of rat brains. TRH produces gastric erosions, increases in acid secretion, and slow contractions, while CRF has the opposite effects. One of the major sites of interaction of the two peptides is in the dorsal motor complex of the vagus nerve. TRH increases serotonin (5-HT) secretion into the stomach. 5-HT counter-regulates acid secretion and slow contractions. Many other peptides stimulate or inhibit gastric acid secretion.

From simplicity to complexity (1950-1990): the case of peptic ulceration--I. Human studies

The problem of the psychobiology of human peptic ulceration has become very much more complicated in the past 20 years, once it was realized that it was not one disease but many. It is recognized that 29 different forms exist. Two common but distinct forms of the disease are characterized by elevated or normal levels of pepsinogen-I. In a third form elevated levels of pepsinogen-II occur; however, this particular increase imparts more of a risk by a factor of 3 for gastric than for duodenal ulcer. In the light of such facts, all studies on the psychological characteristics and social contexts that characterize the onset of the disease must be reevaluated. In addition, a number of different pathophysiological disturbances of the regulation of gastric acid secretion, motility, and bicarbonate secretion characterize patients with the disease, and further subdivide patients with increased or normal pepsinogen-I levels.

CRF microinjected into the dorsal vagal complex inhibits TRH analog- and kainic acid-stimulated gastric contractility in rats

The effect of CRF microinjected into the dorsal vagal complex (DVC) on centrally-stimulated gastric contractility was investigated in fasted, urethane-anesthetized rats. Miniature strain gauge force transducers were acutely implanted on the corpus of the stomach and contractility was analyzed by computer. Microinjection of the stable thyrotropin-releasing hormone (TRH) analog, RX 77368, (26 pmol) into the DVC induced a 12.2-fold stimulation of gastric contractility within 30 min. Corticotropin-releasing factor (CRF) (63-210 pmol) microinjected into the DVC concomitantly with RX 77368 (26 pmol) induced a dose-related inhibition of stimulated gastric contractility. Neither CRF alone (210 pmol) nor vehicle modified basal gastric contractility. Microinjection of kainic acid (141 pmol) into the raphe pallidus nucleus induced a 3.6-fold stimulation of gastric contractility after 45 min. This stimulation was suppressed by bilateral microinjection of CRF (105 pmol/site) into the DVC. These results demonstrate that CRF acts in the DVC to inhibit centrally-stimulated gastric contractility and suggest that TRH and CRF may interact in the DVC to regulate gastric motor function.

Molecular cloning of the mitochondrial aldehyde dehydrogenase gene of Saccharomyces cerevisiae by genetic complementation

Mutants of Saccharomyces cerevisiae deficient in mitochondrial aldehyde dehydrogenase (ALDH) activity were isolated by chemical mutagenesis with ethyl methanesulfonate. The mutants were selected by their inability to grow on ethanol as the sole carbon source. The ALDH mutants were distinguished from alcohol dehydrogenase mutants by an aldehyde indicator plate test and by immunoscreening. The ALDH gene was isolated from a yeast genomic DNA library on a 5.7-kb insert of a recombinant DNA plasmid by functional complementation of the aldh mutation in S. cerevisiae. An open reading frame which specifies 533 codons was found within the 2.0-kb BamHI-BstEII fragment in the 5.7-kb genomic insert which can encode a protein with a molecular weight of 58,630. The N-terminal portion of the protein contains many positively charged residues which may serve as a signal sequence that targets the protein to the mitochondria. The amino acid sequence of the proposed mature yeast enzyme shows 30% identity to each of the known ALDH sequences from eukaryotes or prokaryotes. The amino acid residues corresponding to mammalian cysteine 302 and glutamates 268 and 487, implicated to be involved at the active site, were conserved. S. cerevisiae ALDH was found to be localized in the mitochondria as a tetrameric enzyme. Thus, that organelle is responsible for acetaldehyde oxidation, as was found in mammalian liver.

Stressful experience and cardiorespiratory disorders

Ever since Selye's time, the belief has persisted that the outcome of stressful experience is disease. The likelihood of this eventuality is increased when the experience is damaging, unavoidable, or uncontrollable. However, in most stressful instances, these conditions do not occur. The experience either is overcome or produces disturbances in physiological functions without structural change. The prevalence of "functional" disorders are far more common in medical practice than is disease. Among the most interesting of these is the hyperventilation syndrome, which may mimic or be confused with ischemic heart disease. Its symptomatology and physiology are complex. The syndrome may produce coronary vasospasm, but it may also complicate ischemic heart disease. It is even believed that chronic hyperventilation may be a risk factor for ischemic heart disease. Stressful experience consisting of various tasks and challenges may also produce myocardial perfusion deficits in ischemic heart disease, presumably secondary to vasospasm. These deficits are in turn considerably more frequent in any one patient than ST segment changes in the electrocardiogram or the incidence of angina pectoris. Vasospasm is in turn related to cardiac arrhythmias, which may occur with ischemic heart disease during a variety of stressful experiences and during outbursts of anger. Finally, the role of stressful experience in inciting ischemic heart disease and its complications remains moot.

Effects of protein size on the rate of import of the precursors of aldehyde dehydrogenase and ornithine transcarbamylase into rat liver mitochondria

It is known that a signal peptide is required for the import of a protein into mitochondrial matrix. It is also known that a signal peptide can be attached to any protein and allow it to be imported. We recently reported that the rate of import of rat liver mitochondrial aldehyde dehydrogenase precursor was slower than that of ornithine transcarbamylase precursor (Wang TTY, Farrés J, and Weiner H. Arch Biochem Biophys 272, 440-449, 1989). It was not known if the difference in the rate of import was related to the fact that the mature portion of aldehyde dehydrogenase is larger (500 amino acids compared with 322 amino acids) or because the signal peptides were different. We further showed that treatment of the mitochondria with alcohols caused an inhibition of the import of the precursor of aldehyde dehydrogenase but not that of ornithine transcarbamylase. In the present study we constructed chimeric proteins that contained the signal peptide from one precursor protein and the mature portion from the other. We found that the rate of import was related to the overall size of the precursor protein. Consistent with this observation was finding that a truncated aldehyde dehydrogenase precursor, which contained 317 amino acids, was imported more rapidly than was the authentic precursor. Consistent with this finding was the fact that butanol caused the inhibition of only the large precursor proteins. Thus, it appears that size of the protein being imported is a major determinant of the rate at which a precursor protein is imported into mitochondria.

Bombesin microinjected into the dorsal vagal complex inhibits TRH-stimulated gastric contractility in rats

The effects of centrally injected bombesin on central and peripheral stimulated gastric contractility were investigated in fasted urethane-anesthetized rats. Miniature strain gauge force transducers were acutely implanted on the corpus of the stomach and gastric contractility was analyzed by computer. Intracisternal injection of the stable thyrotropin-releasing hormone (TRH)-analog RX 77368 (77 pmol) induced a stimulation of gastric contractility for 40 min. Intracisternal injection of bombesin (62-620 pmol) followed 30 min later by that of RX 77368 resulted in a dose-related inhibition of the TRH-analog-induced gastric contractility. Intracisternal injection of bombesin (620 pmol) did not modify gastric contractility stimulated by intravenous carbachol. Stimulation of gastric contractility induced by TRH-analog microinjected into the dorsal vagal complex (DVC) was dose-related suppressed by concomitant injections of bombesin (6.2-620 pmol). Neither bombesin alone (6.2 pmol) nor vehicle modified basal gastric contractility. These results demonstrate that bombesin acts within the brain to inhibit vagally stimulated gastric contractility and that the DVC is a sensitive site for bombesin inhibitory action. These findings suggest a possible interaction between TRH and bombesin in the central vagal regulation of gastric contractility.

2D NMR and structural model for a mitochondrial signal peptide bound to a micelle

The 19 amino acid signal peptide of rat liver aldehyde dehydrogenase, possessing a lysine substitution for an arginine and containing 3 extra amino acid residues at the C terminus, was studied by two-dimensional NMR in a dodecylphosphocholine micelle. In this membrane-like environment, the peptide contains two alpha-helical regions, both of which are amphiphilic, separated by a hinge region. The helix located closer to the C terminus is more stable than is the helix located near the N terminus. This suggests that the hydrophobic face of the C-terminal helix is buried within the hydrophobic region of the micelle. On the basis of these results a general model for protein translocation is presented in which the C-terminal amphiphilic helix of the signal region in the preprotein first binds to the mitochondrial membrane and then diffuses to the translocation receptor. The receptor then recognizes the N-terminal helix of the signal region, which is not anchored to the membrane. To explain how this signal peptide was imported into isolated mitochondria in the absence of energy or receptor protein [Pak, Y. K., & Weiner, H. (1990) J. Biol. Chem. 265, 14298-14307], a model for signal peptide translocation across a membrane barrier without the need for auxiliary membrane proteins is proposed. In this model the faces of the two helices fold upon each other, resulting in the mutual shielding of positively charged residues by the complementary hydrophilic face of the other amphiphilic helix.

Import of chemically synthesized signal peptides into rat liver mitochondria

The signal peptides of pre-aldehyde dehydrogenase (22-mer) and pre-ornithine transcarbamylase (27-mer) were chemically synthesized and their imports into rat liver mitochondria were studied. Both signal peptides were imported rapidly (within 2 min) in the absence of a membrane potential, exogenous ATP, or rabbit reticulocyte lysate. Signal peptides also were imported into mitochondria treated with a low concentration of trypsin which removed the outer membrane proteins. It was concluded that the chemically synthesized signal peptide could be imported differently than the precursor proteins. The imported signal peptide were found to be associated with both outer and inner membranes. Pulse-chase experiments showed that the import was unidirectional and that the signal peptides associated with inner membranes increased during the chase time. The signal peptides inhibited import of precursor proteins to different extents. Association of signal peptides with inner membrane near or at translocator sites might result in inhibition of precursor import.

Effects of alcohol on the import of aldehyde dehydrogenase precursor into rat liver mitochondria

We previously showed that incubation of rat liver mitochondria with alcohols resulted in the inhibition of the import of aldehyde dehydrogenase precursor but not that of ornithine transcarbamylase precursor (Wang TTY, Farrés J, and Weiner H: Arch Biochem Biophys 272:440-449, 1989). The time required for inhibition of import to occur was now measured with ethanol (200 mM) and butanol (100 mM) at 0 degree and 30 degrees C. It required approximately 30 min to achieve 50% inhibition with butanol and 50 min with ethanol. To further substantiate the membrane perturbing effects of alcohols, we also examined the effect of oleic acid on import. We found that incubation of mitochondria with oleic acid (0-100 microM) resulted in inhibition of aldehyde dehydrogenase precursor import in a dose response fashion. In addition to in vitro effects of alcohols on import, we conducted a preliminary study on import of protein into liver mitochondria isolated from rats fed ethanol. We found that the rate of aldehyde dehydrogenase precursor import into liver mitochondria isolated from ethanol fed rats was identical to that from control. The results are consistent with finding that the activity and amount of aldehyde dehydrogenase was the same in mitochondria isolated from the alcohol-fed or control animals.

Endogenous serotonin produces an inhibitory tone on vagally stimulated gastric function

The effect of depletion of serotonin stores on vagally stimulated gastric acid secretion and motility was studied in rats. Pretreatment of rats with parachlorophenylalanine (p-CPA) produced a 57% reduction in the intraluminal gastric release of serotonin and a 43-100% potentiation of the gastric acid secretory response elicited by intracisternal injection of the stable TRH analogue RX 77368 in conscious pylorusligated rats or in urethane-anesthetized rats with an acute gastric fistula. p-CPA also enhanced the vagally stimulated gastric acid output produced by intravenous injection of baclofen. In contrast, p-CPA pretreament had no effect on gastric acid secretion stimulated by bethanechol, histamine, or pentagastrin. Selective depletion of central serotonin stores by the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) given alone or combined with parachloroamphetamine pretreatment did not alter RX 77368-stimulated gastric acid secretion. In addition, gastric contractility stimulated by intracisternal injection of RX 77368 was significantly enhanced by p-CPA but not by 5,7-DHT pretreatment; whereas the contractile response to carbachol was not altered by p-CPA pretreatment. These results suggest that depletion of peripheral but not central serotonergic stores potentiates gastric acid secretion and contractility stimulated by vagally, but not peripherally, acting gastric stimulants. Thus, peripheral serotonin may exert an inhibitory tone on vagally stimulated gastric acid secretion and motility in the rat.

[The organism in health and disease. On the path to an integrated biomedical model: sequelae of the theory of psychosomatic medicine]

Traditional Western biomedicine emphasizes changes in structure as explanations of disease, that are produced by single causes. It seeks to understand the proximate, molecular mechanisms of disease. The consequences of this line of thought are varied and many, and are not the purpose of this essay. Psychosomatic medicine research has always been more concerned with a broader and more integrated perspective in health, illness and disease. It has attempted to study and understand persons in terms of the behaviors of interacting systems - the physiology of the organism. In the past 20 years a language has evolved that speaks of the organism's functions in dynamic, time-related terms. Both phenomenologically and mathematically functions can be described in terms of rhythms which with disease undergo change. Each function has its own characteristic features (amplitude, frequency and form) it is frequency modulated. These rhythms are the product of oscillators, and/or positive and negative or mixed feedback systems. When perturbed they undergo changes in features. Many rhythms (e.g. circadian ones) are under environmental control, or are entrained by the environment and by social relationships.