GLUCOCORTICOID STIMULATION OF THE BIOSYNTHESIS OF GLUTAMIC-ALANINE TRANSAMINASE

Plasma metabolomic profile varies with glucocorticoid dose in patients with congenital adrenal hyperplasia

Glucocorticoid replacement therapy is the mainstay of treatment for congenital adrenal hyperplasia (CAH) but has a narrow therapeutic index and dose optimisation is challenging. Metabolomic profiling was carried out on plasma samples from 117 adults with 21-hydroxylase deficiency receiving their usual glucocorticoid replacement therapy who were part of the CaHASE study. Samples were profiled by using hydrophilic interaction chromatography with high resolution mass spectrometry. The patients were also profiled using nine routine clinical measures. The data were modelled by using both multivariate and univariate statistics by using the clinical metadata to inform the choice of patient groupings. Comparison of 382 metabolites amongst groups receiving different glucocorticoid doses revealed a clear distinction between patients receiving ≤5 mg (n = 64) and >5 mg (n = 53) daily prednisolone-equivalent doses. The 24 metabolites which were statistically significantly different between groups included free fatty acids, bile acids, and amino acid metabolites. Using 7 metabolites improved the receiver operating characteristic with area under the curve for predicting glucocorticoid dose of >0.9 with FDR adjusted P values in the range 3.3 E-04 -1.9 E-10. A combination of seven plasma metabolite biomarkers readily discriminates supraphysiological glucocorticoid replacement doses in patients with CAH.

A novel mixed integer programming for multi-biomarker panel identification by distinguishing malignant from benign colorectal tumors

Multi-biomarker panels can capture the nonlinear synergy among biomarkers and they are important to aid in the early diagnosis and ultimately battle complex diseases. However, identification of these multi-biomarker panels from case and control data is challenging. For example, the exhaustive search method is computationally infeasible when the data dimension is high. Here, we propose a novel method, MILP_k, to identify serum-based multi-biomarker panel to distinguish colorectal cancers (CRC) from benign colorectal tumors. Specifically, the multi-biomarker panel detection problem is modeled by a mixed integer programming to maximize the classification accuracy. Then we measured the serum profiling data for 101 CRC patients and 95 benign patients. The 61 biomarkers were analyzed individually and further their combinations by our method. We discovered 4 biomarkers as the optimal small multi-biomarker panel, including known CRC biomarkers CEA and IL-10 as well as novel biomarkers IMA and NSE. This multi-biomarker panel obtains leave-one-out cross-validation (LOOCV) accuracy to 0.7857 by nearest centroid classifier. An independent test of this panel by support vector machine (SVM) with threefold cross validation gets an AUC 0.8438. This greatly improves the predictive accuracy by 20% over the single best biomarker. Further extension of this 4-biomarker panel to a larger 13-biomarker panel improves the LOOCV to 0.8673 with independent AUC 0.8437. Comparison with the exhaustive search method shows that our method dramatically reduces the searching time by 1000-fold. Experiments on the early cancer stage samples reveal two panel of biomarkers and show promising accuracy. The proposed method allows us to select the subset of biomarkers with best accuracy to distinguish case and control samples given the number of selected biomarkers. Both receiver operating characteristic curve and precision-recall curve show our method's consistent performance gain in accuracy. Our method also shows its advantage in capturing synergy among selected biomarkers. The multi-biomarker panel far outperforms the simple combination of best single features. Close investigation of the multi-biomarker panel illustrates that our method possesses the ability to remove redundancy and reveals complementary biomarker combinations. In addition, our method is efficient and can select multi-biomarker panel with more than 5 biomarkers, for which the exhaustive methods fail. In conclusion, we propose a promising model to improve the clinical data interpretability and to serve as a useful tool for other complex disease studies. Our small multi-biomarker panel, CEA, IL-10, IMA, and NSE, may provide insights on the disease status of colorectal diseases. The implementation of our method in MATLAB is available via the website: http://doc.aporc.org/wiki/MILP_k.

Intra- and interprotein phosphorylation between two-hybrid histidine kinases controls Myxococcus xanthus developmental progression

Histidine-aspartate phosphorelay signaling systems are used to couple stimuli to cellular responses. A hallmark feature is the highly modular signal transmission modules that can form both simple "two-component" systems and sophisticated multicomponent systems that integrate stimuli over time and space to generate coordinated and fine-tuned responses. The deltaproteobacterium Myxococcus xanthus contains a large repertoire of signaling proteins, many of which regulate its multicellular developmental program. Here, we assign an orphan hybrid histidine protein kinase, EspC, to the Esp signaling system that negatively regulates progression through the M. xanthus developmental program. The Esp signal system consists of the hybrid histidine protein kinase, EspA, two serine/threonine protein kinases, and a putative transport protein. We demonstrate that EspC is an essential component of this system because ΔespA, ΔespC, and ΔespA ΔespC double mutants share an identical developmental phenotype. Neither substitution of the phosphoaccepting histidine residue nor deletion of the entire catalytic ATPase domain in EspC produces an in vivo mutant developmental phenotype. In contrast, substitution of the receiver phosphoaccepting residue yields the null phenotype. Although the EspC histidine kinase can efficiently autophosphorylate in vitro, it does not act as a phosphodonor to its own receiver domain. Our in vitro and in vivo analyses suggest the phosphodonor is instead the EspA histidine kinase. We propose EspA and EspC participate in a novel hybrid histidine protein kinase signaling mechanism involving both inter- and intraprotein phosphotransfer. The output of this signaling system appears to be the combined phosphorylated state of the EspA and EspC receiver modules. This system regulates the proteolytic turnover of MrpC, an important regulator of the developmental program.

Advances in protein turnover analysis at the global level and biological insights

The concept of a dynamic state of body constituents, a precursor of the modern term of proteome dynamics, was conceived over a century ago. But, not until recently can we examine the dynamics of individual "constituents" for example, proteins at a truly global level. The path of advancement in our understanding of protein turnover at the global level is marked by the introduction of some key technological innovations. These methods include the isotopic tracer technique in the 1930s, the two-dimensional gel electrophoresis technique in the 1970s, the sector mass spectrometer that could analyze isotopomers of peptides in the early 1990s, the 2D gel/MALDI-TOF proteomics technology in the late 1990s, the booming liquid chromatography/mass spectrometry proteomics technology in this decade, and the recently emerging protein-tagging approaches that offer single-cell resolution for protein turnover measurements. The long-standing inquiry raised in the 1950s about the existence of a dynamic state in different organisms at different physiological conditions can now be answered with an individual "constituent" resolution on a truly global scale. Now it appears that protein degradation is not necessarily an end to the protein function. Rather, it can be the start of a new function because protein degradation clears the way for the action of other proteins. Protein turnover participates in a multi-layer complex regulatory network and shares equal importance with gene transcription and protein translation. The advances in technologies for protein turnover analysis and the improved understanding of the biological role of protein turnover will likely help to solve some long-standing biomedical problems such as the tuberculosis disease that at the present day still affects one-third of the world population.

The early effects of short-term dexamethasone administration on hepatic and serum alanine aminotransferase in the rat

Dexamethasone (DEXA) administration has been associated with serum alanine aminotransferase (ALT) elevations that may result from enhanced ALT expression. The aim of our current study was to compare liver vs. serum ALT activity and to examine the onset of any hepatocellular changes. Groups of 4 male Sprague-Dawley rats were administered a single dose of DEXA or corn oil at 12, 16, and 24 h prior to euthanasia or once-daily for 2, 3, or 4 days. All (nonfasted) rats were necropsied together on Day 5. While DEXA incrementally increased liver ALT activity in the 1-, 2-, 3-, and 4-day treatment groups (maximal, 3.7-fold), liver aspartate aminotransferase (AST) never exceeded 1.4-fold over control. Significant hepatic glycogen elevations were detected after DEXA treatment, which correlated with microscopic observations. Serum ALT, AST, sorbitol dehydrogenase, and glutamate dehydrogenase (GLDH) increased after 2, 3, and 4 days of DEXA dosing (1.3-10.3-fold). DEXA-related necropsy findings included pale livers consistent with glycogen deposition. The relative percent liver to body weight was elevated in all DEXA-treated rats. Hepatocellular necrosis was observed in 1/4 rats at 12 h, 2/4 rats at 2 days, 4/4 rats at 3 days, and 3/4 rats at 4 days. DEXA treatment <2 days failed to produce consistent evidence of hepatic injury, as detected by serum biomarkers and pathology assessment. However, early DEXA treatment did correlate with apparent ALT induction. Ultimately, this may explain some early asymptomatic serum ALT elevations seen clinically.

Liver injury model induced in mice by a cellular immunologic mechanism--study for use in immunopharmacological evaluations

Various drugs for clinical hepatitis were applied to a new model of liver injury induced in mice by delayed-type hypersensitivity to picryl chloride (PCI-DTH). The hepatoprotective agent, biphenyl dimethyl dicarboxylate showed a remarkable improvement against the elevation of serum transaminase levels as well as the histopathological changes when given during the induction phase but not during the effector phase of DTH reaction. Cyclophosphamide (Cy), an immunosuppressive agent, significantly inhibited the enzymatic elevation given in both induction and effector phases. However, Cy did not affect the sustaining of liver injury 4 weeks after the liver injury eliciting. Moreover, the consecutive administration of prednisolone (Pred), in both induction phase and sustaining process of liver injury, conversely caused a more severe liver damage. Such exacerbation by Pred might be resulted from its toxic action to hepatocytes. As an immunomodulatory and antiinflammatory agent, glycyrrhizin remarkably improved the sustaining process but not the acute phase of the liver injury. Krestin and malotilate also showed an improving effect on the sustaining development of liver injury. These findings that most of above drugs showed an improving action in their respective manner suggest that this model may be useful for the pharmacological evaluation of drugs especially immunomodulating agents for hepatitis.

Exercise interrupts ongoing glucocorticoid-induced muscle atrophy and glutamine synthetase induction

This study was undertaken to determine whether regular endurance exercise is a deterrent to a developing state of muscle atrophy from glucocorticoids and to evaluate whether the contractile activity antagonizes the hormonal actions on glutamine synthetase, alanine aminotransferase, and cytosolic aspartate aminotransferase (cAspAT). Adult female rats were administered cortisol acetate (CA, 100 mg/kg body wt) or an equal volume of the vehicle solution for up to 15 days. Exercise (treadmill running at 31 m/min, 10% grade, 90 min/day) was introduced after 4 days of CA treatment, at which time plantaris and quadriceps muscle mass had been reduced to 90% of control levels. Running for 11 consecutive days prevented 40 mg of the 90-mg loss and 227 mg of the 808-mg loss that were subsequently observed in plantaris and quadriceps muscles, respectively, in the sedentary animals. Glutamine synthetase mRNA and enzyme activity were elevated threefold by glucocorticoid treatment in the deep quadriceps (fast-twitch red) muscles after 4 days. Initiating exercise completely interfered with the further hormonal induction (to approximately 5-fold) of this enzyme and, after 11 consecutive days of the exercise regimen, glutamine synthetase mRNA and enzyme activity were 58 and 68% of values from CA-treated sedentary animals. In vehicle-treated groups, basal levels of glutamine synthetase expression were also diminished by exercise to approximately 40% of the values in sedentary controls. Hormone treatment did not alter either aminotransferase enzyme activity but reduced cAspAT mRNA in fast-twitch red muscles by 50%. Exercise abolished the glucocorticoid effect on cAspAT mRNA.(ABSTRACT TRUNCATED AT 250 WORDS)

The kinetics of mammalian gene expression

When rates of transcription from specific genes change, delays of variable length intervene before the corresponding mRNAs and proteins attain new levels. For most mammalian genes, the time required to complete transcription, processing, and transport of mRNA is much shorter than the period needed to achieve a new, steady-state level of protein. Studies of inducible genes have shown that the period required to attain new levels of individual mRNAs and proteins is related to their unique half-lives. The basis for this is a physical principle that predicts rates of accumulation of particles in compartmental systems. The minimum period required to achieve a new level is directly proportional to product half-lives because rates of decay control the ratio between the rate of synthesis and the concentration of gene products at steady state. This kinetic model suggests that sensitivity of gene products to degradation by ribonucleases and proteinases is an important determinant of the time scale of gene expression.

Chemical kinetics of induced gene expression: activation of transcription by noncooperative binding of multiple regulatory molecules

A chemical kinetics model is described for the regulation of gene expression by the progressive binding of regulatory molecules to specific binding sites on DNA. Chemical rate equations are formulated and solved for the accumulation of regulatory molecules on DNA, the change in the level of induced mRNA, and the change in the level of the encoded protein in the activated tissue. Some special cases are examined, including that of an activation threshold created by a requirement for the binding of a minimum number of regulatory molecules prior to gene activation. Experimental data for several hormone-activated genetic systems are analyzed in the frame of the proposed model, and kinetic parameters are predicted. The model accounts for a number of experimental characteristics of hormone-inducible genetic systems, including the existence of a lag in the time course of mRNA accumulation, the sigmoidal curve of induced mRNA kinetics, the effect of hormone on mRNA stabilization, and the induction parameters observed when hormone analogues are used. The model also provides an explanation for the phenotypes of genetic variants with altered inducibility as changes in the molecular kinetic parameters of gene activity.

Lipogenic enzyme activities in primary cultures of adult mouse hepatocytes

The effects of various unsaturated fatty acids such as oleic (18:1n-9), linoleic (18:2n-6) and arachidonic (20:4n-6) on the activities of fatty acid synthetase (FAS), malic enzyme (ME), glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) all were determined in primary cultures of mouse hepatocytes. Activities of FAS and ME were found to decrease with time in culture regardless of whether hepatocyte donors were fed diets containing polyunsaturated fatty acid-free hydrogenated cottonseed oil (HCTO) or corn oil (CO). On the other hand, while G6PDH activity also declined in cultured hepatocytes obtained from HCTO-fed mice, the activity of this enzyme increased in cells cultured from CO-fed mice. 6PGDH activity was found to increase in hepatocytes obtained from both diet groups. Neither 18:2 nor 20:4 when added to media could alter FAS or ME activities compared with those observed with either 18:1-containing or fatty acid-free media. Since lactic dehydrogenase activity and the rate of incorporation of [3H] leucine into FAS protein were unaltered with time in hepatocyte cultures, the decreased activities of FAS and ME cannot be attributed to a loss in cell viability during culture but rather appear to be specific for those enzymes which respond to diet hormones in vivo.

Synthesis and degradation of interconvertible enzymes. Kinetic equations of a model system

Steady-state and kinetic equations have been developed which characterize the rates of formation, interconversion, and degradation of an enzyme protein subject to reversible phosphorylation. The theoretical model system incorporates separate fractional degradative rate constants for the phosphorylated and dephosphorylated protein species. The classical models for interconvertible enzymes, and for protein turnover, are special limiting situations of the general model presented here.

The molecular basis of the selectivity of protein degradation in stressed senescent barley (Hordeum vulgare cv. Proctor) leaves

The molecular basis for the selectivity of protein degradation has been examined in osmotically stressed and senescent barley leaves. Relatively weak correlations between the in-vivo rate of loss of enzyme activity, and the charge and molecular weight of the enzymes ahve been detected. We interpret these correlations as supporting the view that the selectivity of enzyme degradation is the result of the physical properties of the enzymes being degraded. The weakness of the correlates is taken to mean that a number of properties which contribute to the selectivity are independent of one another. Under in-vitro conditions (autolysis at 0° C), the loss of enzyme activity was weakly correlated with the charge of the enzymes. However, there was a general similarity between the in-vivo pattern of loss of enzyme activity and the in-vitro patterns under a number of conditions. Furthermore double-isotope experiments demonstrated that the in-vivo degradation of soluble protein was reflected by in-vitro degradation under a number of conditions. Consequently we conclude that the selectivity of protein degradation is largely independent of the nature of the proteolytic system.

An investigation of the properties of ornithine aminotransferase after inactivation by the 'suicide' inhibitor aminohexynoate and use of the compound as a probe of intracellullar protein turnover

Ornithine aminotransferase is shown to bind 1 mol of amino[14C]hexynoate per mol of coenzyme in the 'suicide' inactivation process. At the same time the coenzyme pyridoxal phosphate becomes irreversibly bound to the enzyme protein. Apart from the inactivation, the labelled enzyme is indistinguishable from native ornithine aminotransferase by several separation techniques. Because the rate of degradation of the labelled enzyme is the same as that of the normal enzyme it is concluded that loss of coenzyme does not initiate turnover. Free aminohexynoate is rapidly eliminated from the liver, and 70% of the compound is excreted unchanged in 7.5 h. Inactivated ornithine aminotransferase accounts for 11% of the total labelled liver protein and significant amounts of label are found in aspartate aminotransferase which is also extensively inactivated. The rate of return of enzyme activity is determined and found to be more rapid than expected for a process in which the enzyme is synthesized at a constant rate and degraded in a single, first-order process.

Turnover of yeast fructose-bisphosphatase in different metabolic conditions

Earlier work demonstrated that addition of glucose to yeast growing on noncarbohydrate carbon sources sharply reduces the levels of fructose bisphosphatase. This report indicates that the decrease in the levels of fructose bisphosphatase is accompanied by a parallel decrease of cross-reacting material to specific antibody to fructose bisphosphatase. Use of the specific antibody shows that the loss of activity is irreversible and that its reapperance requires synthesis of protein de novo. The protein is highly stable during growth in ethanol (half life about 90 h). Addition of glucose increases the rate of degradation abut 200-fold. It is shown that the values of the rates of synthesis and degradation of fructose bisphosphatase vary with the metabolic situation of the yeast.

Degradation of cadmium-thionein in rat liver and kidney

[3 H] Cystine and 115mCd were incorporated into hepatic and renal Cd-thionein in response to sc administration of 4.4 mumol of Cd2+ containing 115mCd. Cd-thionein-bound 115mCd reached a plateau by 24 and 72 h after the Cd2+ injection in liver and kidney, respectively. The half-life (t1/2) of 3 H-labeled hepatic Cd-thionein was 3.5 d, whereas the average t1/2 of the soluble proteins was 3.7 d. The t1/2 of 3 H-labeled renal Cd-thionein was 3.7 d, whereas the average t1/2 of the soluble renal proteins was 3.8 d. In marked contrast, the 115mCd content of both hepatic and renal Cd-thionein was virtually unchanged, even 9 d after administration of this radionuclide. These data indicate that the protein moiety of metallothionein is degraded, although there appears to be a concomitant rebinding of Cd2+ to nascent thionein polypeptide chains. Thus the lack of metallothionein degradation per se does not account for the long-term retention of Cd2+ in liver and kidney during chronic exposure.

Plasma renin substrate sensitivity to oestrogens and oestrogen metabolism in cirrhosis

Oestrogen stimulation of plasma renin substrate (PRS) was studied in men with alcoholic cirrhosis. PRS values, before and 1, 2, 4 and 6 days after a single oral administration of 100 microgram of an oestrogen derivative, 11beta-methoxy-17-ethynyl-1,3,5(10)-estratriene-3,17beta-diol (Moxestrol), were measured by radioimmunoassay of generated angiotensin I in five men with normal liver function and five men with alcoholic cirrhosis. Basal PRS was 0.93 +/- 0.22 nmol/ml (mean +/- 1 SD) in the normal men and significantly lower (P less than 0.01) in the men with cirrhosis (0.33 +/- 0.14 nmol/ml). Two days after administration of Moxestrol, PRS rose significantly but transiently (P less than 0.05) to 1.41 +/- 0.42 nmol/ml in the normal men and to 0.47 +/- 0.15 in the cirrhotic men, the relative increase (approximately 50%) being similar in both groups. A study of the plasma kinetics and urinary excretion of Moxestrol was also performed to evaluate its metabolic clearance rate and absorption. Since the intestinal absorption of [14C] Moxestrol was not depressed in cirrhotic men, the low PRS values recorded are probably the consequence of hepatocyte dysfunction.

The diverse effects of 5'-bromodeoxyuridine on enzyme activities in cultured H35 hepatoma cells

Reuber (H35) hepatoma cells were grown in medium containing 10(-5)M bromodeoxyuridine (BrdU), which was incorporated into their DNA. Cell growth rate was unaffected by BrdU for the first two generations, after which it was reduced by about 50%. The effect of BrdU incorporation on the activities of several enzymes with rapid turnover rates was examined to test the hypothesis that the synthesis of such enzymes will be preferentially inhibited by BrdU. Tyrosine amino-transferase (TAT) activity decreased by 70% within two generations whereas thymidine kinase activity remained at control values. PEP carboxykinase activity was unchanged during the first generation in BrdU-containing medium but, during the second, its activity increased by at least 30%. Ornithine decarboxylase levels decreased by about 50% only after two generations in the presence of BrdU. There appeared to be no simple relationship between turnover rates and the effect of BrdU on enzyme activity. Incorporation of BrdU was found to inhibit the induction of both TAT and PEP carboxykinase by dexamethasone and to enhance the inhibition of cell growth by this steroid. These results are discussed with respect to possible mechanisms of gene expression and development in both normal and neoplastic cells.

Stimulation of hepatic sodium and potassium-activated adenosine triphosphatase activity by phenobarbital. Its possible role in regulation of bile flow

Since phenobarbital administration produces a profound increase in bile flow without changing bile acid secretion, we examined whether this drug increases the activity of hepatic sodium-potassium-activated ATPase [Na+-K+)-ATPase], the postulated regulating enzyme in the secretion of bile salt independent bile flow. After freeze-thawing to increase substrate accessibility, (Na+-K+) ATPase activity was determined by ouabain inhibition of total ATPase activity. Its activity was highest in isolated liver surface membrane fractions enriched in bile canalicult. Phenobarbital administration significatly increased (Na+-K+)-ATPase activity in both liver surface membrane fractions as well as liver homogenates. This enhanced activity is apparently selective for other membrane phosphatases and the enzyme activity in other tissues is either unaltered or decreased. Kinetic analysis of (Ka+-K+)-ATPase indicates that phenobarbital treatment increased maximum velocity and half-maximum activation constant was unchanged, consistent with activation of latent molecules or an increased number of enzyme molecules. The latter process seems more likely because cycloheximide prevented phenobarbital induction and activators were not demonstrated in vitro. Examination of the full time course of phenobarbital induction to determine whether phenobarbital increased synthesis or decreased degradation was consistent with increased synthesis since the apparent degradation rates were similar with or without phenobarbital treatment. The apparent half-life for (Na+-K+)-ATPase was estimated to be approximately 2.5 days, consistent with liver surface membrane protein turnover. The correlation of changes in bile flow with (Na+-K+)-ATPase was examined under several experimental situations. Phenobarbital caused a parallel increase in each during the 1st 2 days of greatment: thereafter other factors become rate limiting for flow, since enzyme activity doesn't reach a new steady state until 4-days. Consistent with increased sodium-potassium exchange, bile sodium was unchanged while potasium concentrations were significantly reduced. Changes in both bile flow and (Na+-K+)-ATPase induced by phenobarbital are independent of thyroid hormone. These studies support the postulate that (Na+-K+)-ATPase is an important factor in regulation of bile flow. In addition, phenobarbital enhancement of both bile flow and (Na+-K+)-ATPase is dependent upon de novo protein synthesis.

Turnover of cytochrome C in skeletal muscle of green sunfish (Lepomis cyanellus, R.) during thermal acclimation

The concentration of cytochrome c in the skeletal muscle of the green sunfish (Lepomis cyanellus) increases with decreasing temperature of acclimation: 1.51 +/- 0.09, 1.17 +/- 0.03, and 0.98 +/- 0.07 nanomoles per gram wet weight from muscle of animals acclimated to 5 degrees, 15 degrees, and 25 degrees C, respectively. The roles of synthesis and degradation of cytochrome c during thermal acclimation were investigated by measurement of loss of specific radioactivity from cytochrome c and from total mitochondrial heme protein, and by analysis of the rate of change in concentration of cytochrome c. The radioisotope used was 14C-delta-aminolevulinic acid, a non-reutilizable heme precursor. At 25 degrees C, the half-life of cytochrome c was 7.1 days based on radioactivity measurements and 5.6 days based on change in concentration. Statistical analysis showed no significant difference in half-lives obtained by the two methods. The half-life of total mitochondrial heme protein was determined to be 5.7 days on the basis of radioactivity data, under the same conditions. No significant difference was found between the rate of turnover of the heme protein pool from mitochondria and either measurement for cytochrome c at 25 degrees C. At an acclimation temperature of 5 degrees C, the half-life of cytochrome c from skeletal muscle was 13.7 days based upon changes in concentration. At low acclimation temperature, radioactive label was retained in acid-soluble form by fish for many days, precluding measurement of half-life by this technique. Transfer of fish from 25 degrees to 5 degrees C resulted in a rapid decrease of approximately 40% in rates in synthesis of skeletal muscle cytochrome c, and a concomitant decrease in the degradation rate constant for this molecule of approximately 60%. The disproportionality in temperature-sensitivities of these two processes leads to an approximately 50% net increase in the concentration of cytochrome c during acclimation. In transfer from 5 degrees to 25 degrees C, the converse, rapid readjustments in synthetic and degradative parameters occur, resulting in the observed decrease in cytochrome c content.

Degradation of hepatic zinc-thionein after parenteral zinc administration

A low-molecular-weight protein, zinc-thionein, a metallothionein, was implicated as having a regulatory function in zinc metabolism. The half-life (t 1/2) of hepatic zinc-thionein was determined by pulse-labelling with either L-[35S] cystine and/or 65Zn. In two experiments with L-[35S]cystine, the t 1/2 of zinc-thionein was 18h and 19h. Most of the soluble 35S-labelled hepatic proteins had a t 1/2 of 4 days. The t 1/2 of zinc-thionein calculated by using 65Zn was 20h. The close similarity between the calculated and measured t 1/2 values for zinc-thionein suggests that release of Zn2+ from zinc-thionein probably occurs simultaneously with degradation of the protein moiety.

[Relationship between food protein quality and adrenal cortex function. 7. Relationship between activity of selected liver and small intestine hydrolases and adrenal cortex function]

Male Wistar rats received 10% true digestible crude protein of varying quality (maize gluten (MK) = low protein quality; maize gluten + lysine, tryptophan, threonine, isoleucine (MK + AS) = high protein quality) for a period of three weeks. The trial was carried out to investigate the activity of the two enzymes leucine-arylamidase (LNA) and aminotripeptidase (TP) in the liver and the mucosa of the small intestine and that of alpha and gamma amylases and of total amylases in the mucosa of the small intestine in animals exhibiting differences in the functional state of their adrenal cortices (adrenalectomized animals (AE), normal rats (N) and animals receiving additional treatment with cortisol (KS). It was found that mucosal LNA and gamma amylase did not respond to functional changes in the adrenal cortex. Mucosal LNA had a higher activity if the dietary protein was of low quality and a lower activity if the protein quality was high. The level of liver LNA activity was significantly lower in N and KS animals than in AE animals. The highest activity of mucosal and liver TP was found in KS animals; it was lowest in N animals. Statistically significant differences brought about by changes in the quality of dietary proteins were only found to occur in the KS group. The activity of alpha amylase and total amylases was found to be lowest in N animals; it was significantly higher in animals of the AE and KS groups. Animals of the N and KS groups receiving MK + AS exhibited a significantly higher level in their alpha and total amylase activities than animals in the same group receiving MK. Here, the "permissive action" of glucocorticosteroids on metabolically active hydrolases is clearly evident. The pattern of mucosal LNA activity in the small intestine and that of gamma amylase may be regarded as further characteristic evidence for the digestive action of these enzymes. Liver LNA and liver TP as well as mucosal TP and alpha amylase acted like metabolic enzymes.

L-tyrosine: 2-oxoglutarate aminotransferase induction by hydrocortisone in the thymus of the white rat

Hydrocortisone hemisuccinate within 4 hours after in vivo administration produced an increase in precursor incoporation into rat thymus RNA and proteins in the whole animal. From these results, together with information obtained from measurements of the tyrosine aminotransferase activity and the action of mitomycin C administered one hour before the injection of hydrocortisone, it can be concluded that the increase in tissue level of the enzyme, consequent to hydrocortisone treatment, results from an increased rate of biosynthesis of the enzyme, which participates in the catabolic processes of proteins in glucocorticoid sensitive thymus cells.

Rates of degradation and synthesis of glycosidases de novo during growth and differentiation of Dictyostelium discoideum

1. Injection of a purified preparation of beta-N-acetylglucosaminidase from the spent growth medium of myxamoebae of Dictyostelium discoideum into rabbits gave rise to an antibody preparation containing both anti-alpha-glucosidase and anti-beta-acetylglucosaminidase activities. 2. These two activities were shown to reside in different immunoglobulin molecules and it was concluded that the beta-N-acetylglucosaminidase preparation contained trace amounts of highly antigenic alpha-glucosidase. 3. A single precipitin band having beta-N-acetylglucosaminidase activity was formed in Ouchterlony plates when this antibody preparation was tested against extracts obtained from differentiated cells or from myxamoebae grown either axenically or on bacteria. 4. The antibody preparation was used to show that both beta-N-acetylglucosaminidase and alpha-glucosidase molecules are synthesized de novo from isotopically labelled amino acids during both the growth and differentiation phases of the life cycle and to show that neither of these proteins is significantly degraded during the growth phase or during the first 9h of differentiation. 5. The rates of accumulation of these assayable enzyme activities are thus equal to their rates of synthesis during growth and early differentiation. 6. The factors regulating cellular enzyme activity during the life cycle of D. discoideum are discussed.

Induction of dopa (3,4-dihydroxyphenylalanine) decarboxylase in blowfly integument by ecdysone. A demonstration of synthesis of the enzyme de novo

The activity of the enzyme dopa (3,4-dihydroxyphenylalanine) decarboxylase, present in the epidermis cells of blowfly larvae, increases during the late third instar under the influence of the steroid hormone, ecdysone. By using the double-labelling technique and immune precipitation with univalent antibody to dopa decarboxylase, we demonstrated that the increase in enzyme activity was due to a stimulation of synthesis of enzyme molecules de novo. In this respect, the action of ecdysone is similar to the action of other steroid hormones.

Enzyme synthesis in the regulation of hepatic "malic" enzyme activity

A homogeneous preparation of ;malic' enzyme (EC 1.1.1.40) from livers of thyroxine-treated rats was used to prepare in rabbits an antiserum to the enzyme that reacts monospecifically with the ;malic' enzyme in livers of rats in several physiological states. Changes in enzyme activity resulting from modification of the state of the animal are hence due to an altered amount of enzyme protein. The antiserum has been used to precipitate out ;malic' enzyme from heat-treated supernatant preparations of livers from both adult and neonatal rats, in a number of physiological conditions, that had been injected 30min earlier with l-[4,5-(3)H]leucine. The low incorporations of radioactivity into the immunoprecipitable enzyme have permitted the qualitative conclusion that changed enzyme activity in adult rats arises mainly from alterations in the rate of enzyme synthesis. The marked increase in ;malic' enzyme activity that occurs naturally or as a result of thyroxine treatment of the weanling rat is likewise due to a marked increase in the rate of enzyme synthesis possibly associated with a concurrent diminished rate of enzyme degradation.

The rate of adaptation of urea cycle enzymes, aminotransferases and glutamic dehydrogenase to changes in dietary protein intake

1. Measurements were made, at 6 h intervals, of urinary nitrogen output and of the activity of some hepatic enzymes in the rat during adaptation from one level of dietary protein to another. The enzymes measured were arginase (EC3.5.3.1), argininosuccinate lyase (EC4.3.2.1), argininosuccinate synthetase (EC6.3.4.5), glutamate dehydrogenase (EC1.4.1.2) and alanine and aspartate aminotransferases (EC2.6.1.2 andEC2.6.1.1).

2. Completeness of urine collection, which was essential for these experiments, was checked by recovery of injected [131I]iodide.

3. When the dietary protein content was reduced from 135 to 45 g casein/kg, the urinary N output and the activities of the hepatic enzymes reached their new steady-state levels in 30 h. The reverse adaptation, from 45 to 135 g casein/kg, was also complete in 30 h.

4. The rate of change of enzyme activity and the final activity as percentage of initial activity were very similar for all six enzymes, suggesting a common control mechanism. The calculated half-lives of the enzymes were of the order of 7 h, which is very much shorter than those found by previous workers.

5. There was no simple relationship between the activity of the urea cycle enzymes and the amount of N excreted. When an equal amount of gelatin was substituted for casein the N output was doubled but there was no change in the activity of the liver enzymes.

6. The results suggest that the activity of the urea cycle enzymes depends in part on the amount of N available for excretion after the demands for synthesis have been met. The enzymes, however, appear to be present in excess so that an increased N load was not necessarily accompanied by an increase in enzyme activity.