Rat liver alcohol dehydrogenase. II. Quantitative enzyme-linked immunoadsorbent assay

Isolation and characterization of three alcohol dehydrogenase isozymes from Syrian golden hamsters

Electrophoresis of freshly prepared tissue homogenates of the Syrian golden hamster (Mesocricetus auratus) on starch gel followed by activity staining with ethanol as the substrate revealed three major alcohol dehydrogenase (ADH) isozymes. One of these isozymes, TT-ADH, found only in the testes of golden hamsters was previously purified and partially characterized (Keung WM: Biochem. Biophys. Res. Commun. 156:38-45, 1988). The other two, AA- and BB-ADH, which are most abundant in the liver, have now been purified by affinity chromatography on 4-(3-(N-(6-aminocaproyl)amino)propyl)pyrazole-sepharose and testosterone-17 beta-hemisuccinate-agarose. Hamster AA-, BB-, and TT-ADH are all homodimers of molecular weight near 80,000 and each contains 4 atoms of zinc. Amino acid analyses show that BB-ADH is most closely related to the gamma-form of human class I ADH, whereas AA- and TT-ADH are most closely related to the beta-form of the human enzyme. BB-ADH is the only hamster ADH that is active toward sterols and sensitive to testosterone and isoflavone inhibition. These results suggest that hamster BB- and human gamma gamma-ADH also share similar catalytic properties. AA- and TT-ADH are neither active toward sterols nor sensitive to testosterone or isoflavone inhibition; thus, they are functionally different from the human alpha alpha- or gamma gamma-ADHs. Compared with AA- and BB-ADH, TT-ADH exhibits much higher Km values toward primary aliphatic alcohols and cyclohexanol. AA- and BB-ADH share similar substrate specificities toward primary aliphatic alcohols. However, they exhibit different stereospecificities for secondary alcohols. BB-ADH prefers the (R)-(-)-isomer of 2-butanol, whereas AA-ADH prefers the (S)-(-)-isomer. These results further demonstrate that catalytically, hamster BB- and AA-ADH belong to different subfamilies of class I ADH.

DNA-mediated gene transfer into adult rat hepatocytes in primary culture

Proliferation-competent and differentiation-competent adult rat hepatocytes in primary culture were investigated for their ability to express reporter genes (firefly luciferase, bacterial chloramphenicol acetyltransferase, and bacterial beta-galactosidase) driven by tumor virus or eucaryotic promoters that vary in transcriptional efficiency and tissue specificity. Supercoiled plasmid DNA molecules were introduced into the cells by the calcium phosphate coprecipitation protocol of C. Chen and H. Okayama (Mol. Cell. Biol. 7:2745-2752, 1987). Reporter gene expression was virtually restricted to hepatocytes and was efficient (2 to 20% of the cells). The patterns and absolute levels of reporter gene expression depended on assay conditions employed (plasmid concentration [optimal at 2.4 micrograms of DNA per ml] and duration of exposure [optimal between 5 and 10 h]), culture growth cycle stages (lag, log, or stationary phase), properties and tissue specificity of the promoter(s) tested, and composition (and timing of fluid change) of the culture medium with or without the hepatocyte mitogen human transforming growth factor-alpha. Initial observations suggest that during hepatocellular growth transitions, human transforming growth factor-alpha differentially regulates exogenously introduced promoters associated with hepatocyte-specific function and proliferation. These findings provide a simple, fast, and powerful approach to analyzing the molecular and cellular biology of hepatocyte growth control.

DNA-mediated gene transfer into adult rat hepatocytes in primary culture

Proliferation-competent and differentiation-competent adult rat hepatocytes in primary culture were investigated for their ability to express reporter genes (firefly luciferase, bacterial chloramphenicol acetyltransferase, and bacterial beta-galactosidase) driven by tumor virus or eucaryotic promoters that vary in transcriptional efficiency and tissue specificity. Supercoiled plasmid DNA molecules were introduced into the cells by the calcium phosphate coprecipitation protocol of C. Chen and H. Okayama (Mol. Cell. Biol. 7:2745-2752, 1987). Reporter gene expression was virtually restricted to hepatocytes and was efficient (2 to 20% of the cells). The patterns and absolute levels of reporter gene expression depended on assay conditions employed (plasmid concentration [optimal at 2.4 micrograms of DNA per ml] and duration of exposure [optimal between 5 and 10 h]), culture growth cycle stages (lag, log, or stationary phase), properties and tissue specificity of the promoter(s) tested, and composition (and timing of fluid change) of the culture medium with or without the hepatocyte mitogen human transforming growth factor-alpha. Initial observations suggest that during hepatocellular growth transitions, human transforming growth factor-alpha differentially regulates exogenously introduced promoters associated with hepatocyte-specific function and proliferation. These findings provide a simple, fast, and powerful approach to analyzing the molecular and cellular biology of hepatocyte growth control.

Lobular distribution of alcohol dehydrogenase in the rat liver

The hepatic lobular localization of alcohol dehydrogenase was determined in male, female and castrated male rats. Alcohol dehydrogenase immunoreactive protein and activity were increased in female and castrated rats as compared to normal male rats. By immunohistochemistry, alcohol dehydrogenase protein was found localized principally in the perivenous area of the hepatic lobule in all of the animals. Alcohol dehydrogenase activity eluted from the male rat liver, during bidirectional digitonin perfusion, exhibited a pattern characteristic of cytosolic enzymes predominantly localized to the perivenous area. The elution of the enzyme was more rapid during cava-porta than porta-cava perfusion occurring in close association with the elution of glucokinase, an enzyme localized principally in the perivenous area. By contrast, elution of lactate dehydrogenase, which is located predominantly in the periportal area, preceded elution of alcohol dehydrogenase during porta-cava perfusion, but followed it during cava-porta perfusion. These differences were less apparent in the cava-porta than in the porta-cava direction. The predominant localization of alcohol dehydrogenase immunoreactive protein and activity to the perivenous area of hepatic lobule was not affected by sexual difference or increase in the enzyme following castration.

Detection and localization of immunoreactive alcohol dehydrogenase protein in the rat testis

Alcohol dehydrogenase in the testis metabolizes ethanol and a variety of physiological substrates such as dihydrotestosterone and vitamin A. Studies of the localization of enzyme activity in the testis have revealed its presence in either interstitial cells or seminiferous tubules alone or in both places. The purpose of this study was to detect and localize immunoreactive alcohol dehydrogenase in the testis. The testis enzyme had similar antigenicity than the liver enzyme as demonstrated by double immunodiffusion and inhibition titration using antibody to the liver enzyme. The concentration of immunoreactive enzyme protein was 1.7 +/- 0.1 micrograms/mg of cytosol protein in the testis as compared with 9.3 +/- 0.3 micrograms/mg of cytosol protein in the liver. Isoelectric focusing revealed eight isoenzyme bands. Only the three bands with the highest isoelectric points precipitated with antibody to liver alcohol dehydrogenase. By immunohistochemistry using this antibody, the enzyme was localized principally to the Leydig cells which are also the site of steroidogenesis. The presence in the seminiferous tubules of isoenzymes of lower isoelectric point, which do not react with the antibody to the liver enzyme, can not be excluded.

Characteristics of alcohol dehydrogenase in fat-storing (Ito) cells of rat liver

Fat storing (Ito) cells, located in the perisinusoidal spaces of the liver and the main storage site of vitamin A, have been associated with fibrogenesis. The mechanisms of alcoholic liver disease, although mostly unknown, do involve ethanol metabolism. This study examined the ability of fat-storing cells to metabolize ethanol. Alcohol dehydrogenase activity was detected in fat-storing cells of the rat liver. The enzyme was demonstrated also by enzyme-linked immunosorbent assay and immunohistochemical staining. The enzyme in fat-storing cells is similar to the hepatocyte enzyme in its Michaelis-Menten constants for substrates and coenzymes and in the competitive inhibition by ethanol of retinol oxidation. It differs from the hepatocyte enzyme by its greater susceptibility to inhibition by 4-methylpyrazole and by having a single isoelectric point of 9.5 as compared with multiple isoelectric points in the hepatocyte ranging from 6.9 to 8.8. The ability of the fat-storing cell to oxidize ethanol and the inhibitory effect of ethanol on retinol oxidation may be important in the pathogenesis of alcoholic liver disease.

The prevention of sub-surface demineralization of bovine enamel and change in plaque composition by casein in an intra-oral model

The ability of bovine milk phosphoprotein (casein) to be incorporated into plaque, prevent enamel sub-surface demineralization, and affect bacterial composition was determined using a modified intra-oral caries model. The intra-oral model consisted of a removable appliance containing a left and right pair of bovine enamel slabs placed to simulate an approximal area. Supragingival plaque was collected and impacted into the left and right inter-enamel spaces. The left side of the appliance was exposed to various sugar and salt solutions, while the right side was exposed to sugar and casein solutions. Sodium caseinate, the major fraction alpha s1-casein, and a tryptic digest of alpha s1-casein (TD-casein) were studied. Sodium caseinate at a level of 2% w/v in a 3% sucrose-3% glucose-salt solution (pH 7.0) prevented sub-surface enamel demineralization over a ten-day period as shown by microradiography and microhardness. Two exposures of a 2% w/v sodium caseinate, alpha s1-casein, or TD-casein solution (pH 7.0) per day prevented sub-surface enamel demineralization caused by six exposures of a 3% sucrose-3% glucose-salt solution per day over a ten-day period. Intact alpha s1-casein and tryptic peptides were shown immunochemically to be incorporated into the inter-enamel plaque. The incorporation of casein and its breakdown in plaque did not produce a significant change in the amount or composition of plaque bacteria. The ability of casein and tryptic peptides to prevent enamel demineralization was related to their incorporation into plaque, thereby increasing plaque calcium phosphate and acid-buffering capacity by the phosphoseryl, histidyl, glutamyl, and aspartyl residues and indirectly through catabolism by plaque bacteria.

Inhibitory monoclonal antibodies against rat liver alcohol dehydrogenase

Eleven hybridoma clones which secrete monoclonal antibodies against purified rat liver alcohol dehydrogenase (EC 1.1.1.1) were isolated. Antibodies (R-1-R-11) were identified by their ability to bind to immobilized pure alcohol dehydrogenase in an enzyme-linked immunoadsorbent assay, in which antibody R-9 showed the highest binding capacity. Except for R-1 and R-7, all antibodies inhibited catalytic activity of the enzyme isolated from inbred (Fischer-344) or outbred (Sprague-Dawley) strains (R-11 greater than R-9 greater than R-4 greater than R-6 greater than R-10 greater than R-8 greater than R-2 = R-3 = R-5). The inhibition of enzyme activity by antibodies was noncompetitive for ethanol and NAD+, and was dependent on antibody concentration and incubation time. Antibodies R-4, R-9, and R-11 were most effective when enzyme activity was assayed below pH 7.7-7.8, a condition thought to protonate the enzyme's active center. These three antibodies did not inhibit horse liver alcohol dehydrogenase activity, indicating their species specificity. Such antibodies will be useful to delineate structural and functional roles of rat liver alcohol dehydrogenase.

Developmental changes in rat liver alcohol dehydrogenase

Hepatic alcohol dehydrogenase activity and mass content change coordinately during development in male rats. Enzyme activity and mass content increase continuously after birth to 100 and 80% of maximal values within 6 weeks (2.6 +/- 0.4 mumole/min/g liver and 92 +/- 20 micrograms/g liver), respectively. When expressed per milligram of soluble proteins, both parameters peak at 3 weeks (0.052 +/- 0.002 mumole/min/mg protein and 2.0 +/- 0.4 micrograms/mg protein) and then decrease gradually to plateau levels. These decreases probably arise from a "surge" in soluble liver protein levels that occurs after weaning. Similar developmental patterns also occur in female rats. These findings are the first quantitative measurements of this enzyme in developing animals.

Rat liver alcohol dehydrogenase. I. Purification and characterization

Alcohol dehydrogenase was purified in 14 h from male Fischer-344 rat livers by differential centrifugation, (NH4)2SO4 precipitation, and chromatography over DEAE-Affi-Gel Blue, Affi-Gel Blue, and AMP-agarose. Following HPLC more than 240-fold purification was obtained. Under denaturing conditions, the enzyme migrated as a single protein band (Mr congruent to 40,000) on 10% sodium dodecyl sulfate-polyacrylamide gels. Under nondenaturing conditions, the protein eluted from an HPLC I-125 column as a symmetrical peak with a constant enzyme specific activity. When examined by analytical isoelectric focusing, two protein and two enzyme activity bands comigrated closely together (broad band) between pH 8.8 and 8.9. The pure enzyme showed pH optima for activity between 8.3 and 8.8 in buffers of 0.5 M Tris-HCl, 50 mM 2-(N-cyclohexylamino)ethanesulfonic acid (CHES), and 50 mM 3-(cyclohexylamino)-1-propanesulfonic acid (CAPS), and above pH 9.0 in 50 mM glycyl-glycine. Kinetic studies with the pure enzyme, in 0.5 M Tris-HCl under varying pH conditions, revealed three characteristic ionization constants for activity: 7.4 (pK1); 8.0-8.1 (pK2), and 9.1 (pK3). The latter two probably represent functional groups in the free enzyme; pK1 may represent a functional group in the enzyme-NAD+ complex. Pure enzyme also was used to determine kinetic constants at 37 degrees C in 0.5 M Tris-HCl buffer, pH 7.4 (I = 0.2). The values obtained were Vmax = 2.21 microM/min/mg enzyme, Km for ethanol = 0.156 mM, Km for NAD+ = 0.176 mM, and a dissociation constant for NAD+ = 0.306 mM. These values were used to extrapolate the forward rate of ethanol oxidation by alcohol dehydrogenase in vivo. At pH 7.4 and 10 mM ethanol, the rate was calculated to be 2.4 microM/min/g liver.