Monoamine oxidase activity in normal and Lesch-Nyhan fibroblasts

Identification and Evaluation of Olive Phenolics in the Context of Amine Oxidase Enzyme Inhibition and Depression: In Silico Modelling and In Vitro Validation

The Mediterranean diet well known for its beneficial health effects, including mood enhancement, is characterised by the relatively high consumption of extra virgin olive oil (EVOO), which is rich in bioactive phenolic compounds. Over 200 phenolic compounds have been associated with Olea europaea, and of these, only a relatively small fraction have been characterised. Utilising the OliveNetTM library, phenolic compounds were investigated as potential inhibitors of the epigenetic modifier lysine-specific demethylase 1 (LSD1). Furthermore, the compounds were screened for inhibition of the structurally similar monoamine oxidases (MAOs) which are directly implicated in the pathophysiology of depression. Molecular docking highlighted that olive phenolics interact with the active site of LSD1 and MAOs. Protein-peptide docking was also performed to evaluate the interaction of the histone H3 peptide with LSD1, in the presence of ligands bound to the substrate-binding cavity. To validate the in silico studies, the inhibitory activity of phenolic compounds was compared to the clinically approved inhibitor tranylcypromine. Our findings indicate that olive phenolics inhibit LSD1 and the MAOs in vitro. Using a cell culture model system with corticosteroid-stimulated human BJ fibroblast cells, the results demonstrate the attenuation of dexamethasone- and hydrocortisone-induced MAO activity by phenolic compounds. The findings were further corroborated using human embryonic stem cell (hESC)-derived neurons stimulated with all-trans retinoic acid. Overall, the results indicate the inhibition of flavin adenine dinucleotide (FAD)-dependent amine oxidases by olive phenolics. More generally, our findings further support at least a partial mechanism accounting for the antidepressant effects associated with EVOO and the Mediterranean diet.

Lesch-Nyhan disease causes impaired energy metabolism and reduced developmental potential in midbrain dopaminergic cells

Mutations in HPRT1, a gene encoding a rate-limiting enzyme for purine salvage, cause Lesch-Nyhan disease which is characterized by self-injury and motor impairments. We leveraged stem cell and genetic engineering technologies to model the disease in isogenic and patient-derived forebrain and midbrain cell types. Dopaminergic progenitor cells deficient in HPRT showed decreased intensity of all developmental cell-fate markers measured. Metabolic analyses revealed significant loss of all purine derivatives, except hypoxanthine, and impaired glycolysis and oxidative phosphorylation. real-time glucose tracing demonstrated increased shunting to the pentose phosphate pathway for de novo purine synthesis at the expense of ATP production. Purine depletion in dopaminergic progenitor cells resulted in loss of RHEB, impairing mTORC1 activation. These data demonstrate dopaminergic-specific effects of purine salvage deficiency and unexpectedly reveal that dopaminergic progenitor cells are programmed to a high-energy state prior to higher energy demands of terminally differentiated cells.

Constitutional mechanisms of vulnerability and resilience to nicotine dependence

The core nature of nicotine dependence is evident in wide variations in how individuals become and remain smokers. Individuals with pre-existing behavioral traits are more likely to develop nicotine dependence and experience difficulty when attempting to quit. Many molecular factors likely contribute to individual variations in the development of nicotine dependence and behavioral traits in complex manners. However, the identification of such molecules has been hampered by the phenotypic complexity of nicotine dependence and the complex ways molecules affect elements of nicotine dependence. We hypothesize that nicotine dependence is, in part, a result of interactions between nicotine and pre-existing behavioral traits. This perspective suggests that the identification of the molecular bases of such pre-existing behavioral traits will contribute to the development of effective methods for reducing smoking dependence and for helping smokers to quit.

Relationship between monoamine oxidase (MAO) A specific activity and proportion of human skin fibroblasts which express the enzyme in culture

Total deficiency of monoamine oxidase A (MAO-A) in affected males of a single, human kindred appears to be associated with mild mental retardation and significant behavioral anomalies. Though total MAO-A deficiency appears to be rare, the extent and significance of individual variation in monoamine oxidase A activity in human populations is unclear. Since MAO-A activity is undetectable in blood cells, most systematic surveys of individual variation MAO-A activity have compared enzyme activity in human fibroblasts cultured from skin biopsies. Surprisingly, MAO-A activity in skin fibroblast cultures from unrelated donors ranges over 100-fold. It has been suggested that this extreme variation in fibroblast MAO-A activity between donors reflects individual, genetic variation in the regulation of MAO-A in fibroblasts. I have found from studies with immunofluorescence microscopy and flow cytometry that the proportion of MAO-A+ cells in fibroblast cultures is (a) highly variable between cultures, (b) a reproducible characteristic of each culture and (c) the primary factor responsible for variation in MAO-A specific activity in whole cell, skin fibroblast homogenates. It has been shown previously that MAO-A activity of a skin fibroblast culture is relatively constant with continued passage prior to cellular senescence. Therefore, these new data raise the possibility that MAO-A expression is confined to a functionally distinct subset of human skin fibroblasts.

Mutational analysis of the human MAOA gene

The monoamine oxidases (MAO-A and MAO-B) are the enzymes primarily responsible for the degradation of amine neurotransmitters, such as dopamine, norepinephrine, and serotonin. Wide variations in activity of these isozymes have been reported in control humans. The MAOA and MAOB genes are located next to each other in the p11.3-11.4 region of the human X chromosome. Our recent documentation of an MAO-A-deficiency state, apparently associated with impulsive aggressive behavior in males, has focused attention of genetic variations in the MAOA gene. In the present study variations in the coding sequence of the MAOA gene were evaluated by RT-PCR, SSCP, and sequencing a mRNA or genomic DNA in 40 control males with > 100-fold variations of MAO-A activity, as measured in cultured skin fibroblasts. Remarkable conservation of the coding sequence was found with only 5 polymorphisms observed. All but one of these were in the third codon position and thus did not alter the deduced amino acid sequence. The one amino acid alteration observed, lys --> arg, was neutral and should not affect the structure of the protein. This study demonstrates high conservation of coding sequence in the human MAOA gene in control males, and provides primer sets which can be used to search genomic DNA for mutations in this gene in males with neuropsychiatric conditions.

Abnormal behavior associated with a point mutation in the structural gene for monoamine oxidase A

Genetic and metabolic studies have been done on a large kindred in which several males are affected by a syndrome of borderline mental retardation and abnormal behavior. The types of behavior that occurred include impulsive aggression, arson, attempted rape, and exhibitionism. Analysis of 24-hour urine samples indicated markedly disturbed monoamine metabolism. This syndrome was associated with a complete and selective deficiency of enzymatic activity of monoamine oxidase A (MAOA). In each of five affected males, a point mutation was identified in the eighth exon of the MAOA structural gene, which changes a glutamine to a termination codon. Thus, isolated complete MAOA deficiency in this family is associated with a recognizable behavioral phenotype that includes disturbed regulation of impulsive aggression.

Evidence for G proteins in rat parotid plasma membranes and secretory granule membranes

G proteins were identified in rat parotid plasma membrane-enriched fractions and in two populations of isolated secretory granule membrane fractions. Both [32P]ADP-ribosylation analysis with bacterial toxins and immunoblot analysis with crude and affinity-purified antisera specific for alpha subunits of G proteins were utilized. Pertussis toxin catalysed the ADP-ribosylation of a 41 kDa substrate in the plasma membrane fraction and both secretory granule membrane fractions. Cholera toxin catalysed the ADP-ribosylation of two substrates with molecular masses of 44 kDa and 48 kDa in the plasma membrane fraction but not in the secretory granule fractions. However, these substrates were detected in the secretory granule fractions when recombinant ADP-ribosylating factor was present in the assay medium. Immunoblot analysis of rat parotid membrane fractions using both affinity-purified and crude antisera revealed strong immunoreactivity of these membranes with anti-Gs alpha, -Gi alpha 1/alpha 2 and -Gi alpha 3 sera. In contrast Gs alpha was the major substrate found in both of the secretory granule fractions. Granule membrane fractions also reacted moderately with anti-Gi alpha 3 antiserum, and weakly with anti-Gi alpha 1/alpha 2 and -G(o) alpha sera. The results demonstrate that the parotid gland membranes express a number of G proteins. The presence of G proteins in secretory granule membranes suggests that they may play a direct role in regulating exocytosis in exocrine glands.

Biochemistry and genetics of monoamine oxidase

This chapter reviews the two mitochondrial flavin containing isozymes of monoamine oxidase. Section 1, "Biochemistry" discusses assays, substrates and inhibitors, phylogenic and tissue distribution, interactions with lipids, nutritional studies, protein structure, kinetic and chemical mechanistic proposals, and biosynthesis. Section 2, "Inheritance" discusses possible genes involved in expression, genetic studies of platelet MAO-B and fibroblast MAO-A, and chromosomal location. Section 3, "Molecular Genetics" reviews the cloning of their cDNAs, their intra- and interspecies homology and structural inferences made from deduced amino acid sequences. Section 4, "Regulation" gives an overview of levels in development and aging, and effect of drugs. The final section 5, "Role in Human Disease" discusses physiological function and effects of altered levels in humans and animal models including complete absence due to a submicroscopic chromosomal deletion in several human patients.

Monoamine oxidases A and B are differentially regulated by glucocorticoids and "aging" in human skin fibroblasts

Two forms of monoamine oxidase (MAO A and MAO B) exist which, although similar in a number of properties, can be distinguished on the basis of their substrate specificity, inhibitor sensitivity, kinetic parameters, and protein structure. These properties were used to study the molecular mechanism(s) by which glucocorticoid hormones and "aging," known to alter MAO activity in vivo, regulated the expression of MAO A and MAO B in cultured human skin fibroblasts. The addition of dexamethasone or hydrocortisone to cultures resulted in a dose- and time-dependent increase in total MAO activity, whereas the removal of hormone from cultures resulted in a time-dependent decrease in activity toward control levels. The response to dexamethasone was affected by culture conditions such as serum concentration, feeding frequency, and cellular "age." Cellular aging, in the absence of hormone, also resulted in increased levels of total MAO activity. The effects of hormones and aging on total MAO activity appeared to be selective for MAO A. The 6- to 14-fold increases in total activity were paralleled by similar increases in the activity and amount of active MAO A but less than 2- to 3-fold increases in the activity and amount of MAO B. Altered synthesis or degradation of the active enzyme appeared to account for the effects of hormones, aging, and various culture conditions on MAO activity. Inhibitor sensitivity, substrate affinity, electrophoretic mobility, and molecular turnover number of either form of the enzyme were not altered during dexamethasone treatment or during cellular aging. However, rates of active MAO synthesis were affected by hormone treatment and feeding frequency, rates of active MAO degradation by serum concentration, and rates of active MAO synthesis or degradation by aging. In summary, we have shown that glucocorticoids and cellular aging selectively affect the amount of MAO A at the level of active enzyme synthesis or degradation. Further, our finding that the expression of the two forms of MAO in human fibroblasts can be independently regulated supports the growing evidence that MAO A and MAO B are separate molecular entities.

Specific [3H]-N-methyl scopolamine binding without cholinergic function in cultured adult skin fibroblasts

Cultured adult skin fibroblasts were studied for binding and functional evidence of muscarinic receptors in order to assess their utility as a model of cholinergic function in affective illness. Saturable, specific, high affinity binding could be demonstrated in intact cells from some cell lines with [3H]-NMS, but not [3H]-QNB, presumably because of intracellular trapping of unbound [3H]-QNB. [3H]-NMS specific binding indicated a single site with a KD of approximately 210 pM. [3H]-NMS was displaced by cholinergic agonists and antagonists with relative affinities similar to muscarinic receptors in brain. Many cell lines, however, showed no specific binding. No functional response to carbachol could be demonstrated with respect to inhibition of isoproterenol-stimulated cyclic AMP formation, stimulation of cyclic GMP formation or stimulation of phosphoinositide hydrolysis in any cell line regardless of either high or no specific [3H]-NMS binding.

Assignment of genes for human monoamine oxidases A and B to the X chromosome

Monoclonal antibodies that immunoprecipitate human monoamine oxidase (MAO) A or human MAO B, but not the corresponding mouse enzymes, were used to assay for the presence of immunoprecipitable MAO A or MAO B (presumably coded by the respective human genes) in mouse-human hybrid somatic cell lines containing small numbers of human chromosomes. The results were as follow: Extracts of a human lymphoblastoid x mouse hepatoma hybrid line that retained the human X chromosome contained immunoprecipitable MAO B, while a similar hybrid line that contained the same human chromosomes, except for the human X, did not. Extracts of a human fibroblast x mouse neuroblastoma hybrid cell line, whose human chromosomal material consisted solely of the X, contained both immunoprecipitable MAO A and MAO B. Extracts of a related hybrid line, whose human chromosomal material consisted solely of an autonomous fragment and a fragment translocated to a mouse chromosome, contained immunoprecipitable MAO A. However, the level of immunoprecipitable MAO B activity in extracts of this hybrid was low or undetectable. Among extracts of 33 human fibroblast x mouse hepatoma hybrids that had been selected for expression of the X-linked human enzyme HPRT, 60% contained immunoprecipitable MAO B. This figure was comparable to the 58% that expressed the X-linked human isozyme for glucose-6-phosphate dehydrogenase (G6PD). When 11 of these hybrid lines, which contained immunoprecipitable MAO B and human HPRT, were selected for loss of HPRT, all lost immunoprecipitable MAO B in addition to HPRT. These data demonstrate that genes controlling the expression of MAO A and MAO B, which can be immunoprecipitated with the human-specific monoclonal antibodies, are located on the human X chromosome. Properties of the immunological epitopes recognized by the monoclonal antibodies suggest that the X-linked genes detected in this study are probably structural genes for the enzymes.

Muscarinic receptors on intact human fibroblasts. Absence of receptor activity in adult skin cells

The intact human fibroblast has been used in clinical and basic research studies of receptor-mediated control of cell function, however there is little information about the relationship between muscarinic receptor density and the regulation of cyclic AMP (cAMP) accumulation. We have compared the muscarinic receptor characteristics of both lung and skin intact fibroblasts at fetal and adult stages of development using carbachol-mediated inhibition of cAMP accumulation and the binding of [3H]quinuclidinyl benzilate (QNB). Prostaglandin E1 (PGE1) stimulated cAMP accumulation in all four cell lines, while carbachol inhibited cAMP accumulation only in the fetal lung, adult lung, and to a lesser extent, the fetal skin. Adult skin fibroblasts did not display significant evidence of inhibitory muscarinic receptor activity. [3H]QNB binding was saturable for the fetal and adult lung, and the fetal skin, yielding Kd values of approximately 0.5 nM for these cell lines. Bmax values were 360 fmol/mg for fetal skin, 600 fmol/mg for adult lung, and 876 fmol/mg for the fetal lung. Specific binding of [3H]QNB to adult skin fibroblasts was found to be low and variable. Comparisons of the Bmax values and maximal inhibitory capacities showed that the receptor density paralleled receptor activity in all cell lines. The lack of muscarinic receptor activity in the adult skin fibroblast was confirmed in several different adult skin cell lines, indicating that the adult skin fibroblast may not be an appropriate model for muscarinic receptor activity in clinical investigations.

Expression of A and B types of monoamine oxidase in differentiated neuroblastoma hybrid cells

The total activities of monoamine oxidase (MAO) and the ratio of type B/type A activities were determined in mouse neuroblastoma N1E-115 cells, and in NX31T and NG108-15 hybrid cells derived from mouse neuroblastoma X rat sympathetic ganglion hybrid or mouse neuroblastoma X rat glioma hybrid cells. N1E-115 and NX31T cells possessed type A activities exclusively, although NG108-15 cells showed both type A (65-90%) and type B (10-35%) MAO activities. The activity of type A MAO in NX31T and N1E-115 cells was relatively constant during culturing periods in the presence or absence of dibutyryl cyclic AMP (Bt2cAMP), whereas total MAO activity and the ratio of type B MAO/type A MAO in NG108-15 cells increased as a function of culture periods. Prostaglandin E1 (PGE1) and theophylline, the best known combination to increase intracellular cyclic AMP content of NG108-15 cells, caused similar increases of MAO and of the type B/type A ratio in NG108-15 cells. The results suggest that MAO activity and expression of MAO B activity are regulated in NG108-15 cells in a cyclic AMP-dependent manner.

Platelet and fibroblast monoamine oxidase in alcoholism

Monoamine oxidase (MAO) activity has been reported to be low in platelets (MAO B) and brain (MAO A and B) of some patients with alcoholism compared to control subjects. Whether the decreased platelet MAO activity found in alcoholism is secondary to the effect of alcohol or exists before alcohol abuse is not clear. The hypothesis that altered MAO A activity is determined by an abnormality in the genetic regulation of the enzyme can be tested by measuring MAO A activity in human fibroblasts cultured under controlled conditions. We first studied the kinetic parameters of platelet MAO B activity in patients hospitalized for treatment of alcoholism. Vmax was 38% lower in the patients (n = 14) than in normal controls (n = 22), but the enzyme affinity (Km) for the substrate tyramine was unchanged. Patients with the five lowest levels of platelet MAO activity had MAO activity measured from fibroblasts cultured from skin punch biopsies. Their fibroblast MAO activity was within the normal range, showing a dissociation between platelet MAO B and fibroblast MAO A activities and suggesting that MAO A activity is not low for genetic reasons in alcoholic subjects who do have low platelet MAO B activity.

Absence of specific binding of several putative neuro-transmitters to human fibroblasts

Fibroblasts were examined for specific binding sites of ten putative neurotransmitters to determine whether this tissue could be used in receptor studies of neurologic and psychiatric disorders. Stereospecific saturable binding was not found for any of the ligands: arginine vasopressin, neurotensin, somatostatin, angiotensin II, thyrotropin-releasing hormone (TRH), alpha-bungarotoxin, LSD, dihydromorphine, muscimol and spiperone.

Monoamine oxidase (MAO) activity as a determinant in human neurophysiology

Several lines of evidence indicate that monoamine oxidase (MAO) activity can regulate levels of biogenic amines and neuronal activity in the nervous system. The two types of MAO activity, A and B, appear to have different domains of activity in the body. Brain tissue has both types of activity, although adrenergic neurons are thought to contain exclusively MAO-A. MAO activity can also be measured in peripheral tissues: MAO-A in cultured skin fibroblasts and placenta, and MAO-B in platelets and lymphocytes. These two types of activity are mediated by different enzyme molecules and are regulated independently by endogenous and exogenous factors including genetic determinants, hormones, and aging. In humans, inhibition of MAO-A activity leads to mood elevation in depressed patients; in contrast, low MAO-B activity in platelets has been associated with an increased susceptibility to psychopathology. In order to assess further the role of MAO activity in human mood and behavior, it will be important to measure both forms of the enzyme independently and to establish correlations between levels of activity and discrete phenotypic traits.

Amine oxidase in human blood vessels and non-vascular smooth muscle

The pattern of amine oxidation was studied in human blood vessels at various stages of development, and in tissues with muscular layers made up predominantly or exclusively of smooth muscle. Specific activity of benzylamine oxidase, present in all vascular tissues examined, was higher in vessels than in other tissue; the enzyme, in organs rich in non-vascular smooth muscle, though lower than in blood vessels, was significantly higher than in striated muscle or connective tissue. The localization of benzylamine oxidase activity in smooth muscle, as opposed to connective tissue, may have important physiological implications.

Differences in the structure of A and B forms of human monoamine oxidase

[3H]Pargyline-labeled polypeptides associated with the A and B types of monoamine oxidase (MAO) activity in human tissues were analyzed by sodium dodecyl sulfate--polyacrylamide gel electrophoresis (SDS-PAGE). [3H]Pargyline was bound to MAO A in a crude mitochondrial fraction from the placental trophoblast of a male newborn and to MAO B in blood platelets from the umbilical vein of the same newborn. [3H]Pargyline was also bound to MAO A and B in a crude mitochondrial fraction from cultured skin fibroblasts of a male adult and to MAO B in blood platelets from the same individual. Specific labeling of proteins associated with type A or type B activity in fibroblast cells was achieved by preincubation with selective B or A inhibitors, respectively. For all tissues, SDS-PAGE of [3H]pargyline-bound samples revealed a labeled protein band of apparent molecular weight 63,000 for MAO A and 60,000 for MAO B. When SDS-solubilized, [3H]pargyline-labeled MAO A and B proteins from the same male newborn were subjected to limited proteolysis and one-dimensional peptide mapping in SDS gels, different patterns of [3H]pargyline-labeled peptides were obtained. These findings indicate that distinct enzyme molecules are associated with the A and B types of human MAO activity.

High-affinity [3H]choline accumulation in cultured human skin fibroblasts

[3H]Choline can be transported across cell membranes by high-affinity (KT less than 5 microM) and low-affinity (KT much greater than 5 microM) systems. High-affinity choline accumulation (HACA) has been demonstrated in synaptosomes made from cholinergic brain regions such as the hippocampus and caudate-putamen. In cell culture, HACA has been demonstrated in glia and avian telencephalon, dissociated spinal cord, and muscle fibroblasts. We examined [3H]choline accumulation in a single normal human fibroblast line cultured from skin biopsy. [3H]Choline accumulation was temperature-dependent and linear with incubation time up to 6 min at 0.125 microM-choline. The apparent KT for [3H]choline was 5 microM, which is similar to that observed in avian fibroblasts. Isoosmotic replacement of Na+ with either Li+ (144 mM) or sucrose (288 mM) severely reduced [3H]choline accumulation (by 70-90%). Pre-incubation with ouabain (100 microM), sodium orthovanadate (100 microM), or 2,4-dinitrophenol (100 microM), or replacement of Ca2+ by Mg2+ had little or no effect on subsequent [3H]choline accumulation. [3H]Choline accumulation was inhibited by hemicholinium-3 (HC-3); after pre-incubation in HC-3 at 37 degrees C for 10 min, the IC50 (at 0.125 microM-choline) was 5.6 microM. The HC-3 sensitivity, Na+ dependence, and low KT suggest that human skin fibroblasts have a high-affinity transport system for choline.

A caution in the use of tritiated substrates for monoamine oxidase assays

A monoamine oxidase assay utilizing generally labeled [3H]serotonin as substrate became nonlinear after only approximately 5% conversion of initial c.p.m. to product. Subsequent analysis showed that a significant proportion of the tritium label was readily exchangeable into water and that monoamine oxidase activity increased release of label as water. The use of generally labeled substrates for oxidase activities is not recommended.

Monoamine oxidase type A in fibroblasts from patients with bipolar depressive illness

No differences in levels of type A monoamine oxidase (MAO) were observed in cultured human skin fibroblasts from nine patients with bipolar depressive illness as compared to 18 age-, sex-, and race-matched controls. All cells were biopsied and cultured under parallel conditions. Fibroblasts from monozygotic twins (three sets) had levels of MAO activity that were highly concordant, indicating that levels measured in fibroblasts are genetically determined. Together these findings suggest that an inherited predisposition to bipolar depressive illness does not involve inherited variations in levels of type A MAO activity. Using a larger control population, a positive correlation was observed between age of donor and level of MAO activity. This finding demonstrates the need for age-matched control and patient groups when comparing levels of type A MAO in fibroblasts.

Properties of monoamine oxidase in control and Lesch-Nyhan fibroblasts

Monoamine oxidase activity of the A type was measured in homogenates of cultured human skin fibroblasts. Twenty-four control lines had activities ranging over fifty-fold with an apparent bimodal distribution. Activity in fibroblasts from 20 patients with the Lesch-Nyhan syndrome fell in the low portion of the normal distribution with a mean activity about 50% that of the control mean (p < 0.05). In a subgroup of control and Lesch-Nyhan lines with levels of enzyme activity from 0.9 to 179 pmol/min/mg protein, monoamine oxidase was similar with respect to apparent Km for tryptamine, thermal stability at 56 C, and sensitivity to clorgyline. Thus the lower mean levels of activity observed in the Lesch-Nyhan as compared to control fibroblasts were not associated with other altered properties of the enzyme. The bimodal distribution of enzyme activity suggests that a genetic polymorphism for monoamine oxidase may control levels of activity expressed in fibroblasts.

Monoamine oxidase and catechol-O-methyltransferase activities in cultured fibroblasts and blood cells from children with autism and the Gilles de la Tourette syndrome

Monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT) activities were measured in cells from children with autism (n = 5) and the Gilles de la Tourette syndrome (n = 5). Monoamine oxidase activities in cultured skin fibroblasts (type A) and platelets (type B) from the same individual were not correlated. COMT activities in fibroblasts and red blood cells showed a negative but not significant correlation (r = -0.42). Fibroblast MAO and COMT activities from patients were similar to values from controls matched for age, race, and sex. Increasing clinical severity of illness in both disorders, however, correlated significantly with higher fibroblast MAE activity. Cultured fibroblasts provide a means of measuring enzyme activities independently of the individual's current physiological and psychological state.