Sexual differentiation of rat liver carbonic anhydrase III

Using radioimmunoassay, the concentration of carbonic anhydrase III in the livers of adult male rats was found to be approx. 30-times greater than that observed in mature females. Castration of male rats led to a marked reduction in liver carbonic anhydrase III concentrations which could be partially restored to control levels by testosterone replacement. Administration of testosterone to ovariectomised female rats induced about a 5-fold increase in liver carbonic anhydrase III concentration. Immunoprecipitation analysis of the products of liver mRNA translation in vitro with antiserum specific for carbonic anhydrase III showed that hormonal control of the levels of carbonic anhydrase III in liver is mediated by changes in the amount of translatable carbonic anhydrase III mRNA. Marked changes in liver carbonic anhydrase III concentrations were also observed in developing and ageing male rats.     

Androgen-linked control of rat liver carbonic anhydrase III

The concentration of carbonic anhydrase III (CAIII) in male rat liver was found to be 30 times greater than that in the female. Castration of male rats led to marked reduction in liver CAIII concentrations which could be partially restored to control levels by testosterone replacement. Marked developmental and senescence changes in liver CAIII were also observed in male rats.     

Hypophysectomy abolishes sexual dimorphism of liver carbonic anhydrase III

Hypophysectomy was found to have no effect on the concentration of carbonic anhydrase III (CAIII) in male rat liver, whereas in the female, CAIII was elevated 10-fold, to male levels.     

Identification of the zinc-binding protein specifically present in male rat liver as carbonic anhydrase III

A zinc (Zn)-binding protein that is present specifically in the livers of male adult rats was detected by HPLC with in-line detection by mass spectrometry (ICP MS). The Zn-binding protein was purified on Sephadex G-75 and G3000SW HPLC columns. and was identified as carbonic anhydrase III (CAIII) based on the amino acid sequence of a peptide obtained on lysyl endopeptidase digestion. CAIII is expressed as one of the major Zn-binding proteins in the livers of male rats in an age-dependent manner, a comparable amount of Zn to that of copper, Zn-superoxide dismutase (Cu,Zn-SOD) being bound to CAIII at 8 weeks of age. Castration at 4 or 8 weeks of age was shown to reduce Zn bound to CAIII to 47.5% of the sham-operated control level, suggesting that the sex-dependent expression of CAIII is partly regulated by a sex hormone, androgen. The concentration of CAIII in the livers of Long-Evans rats with a cinnamon-like coat color (LEC rats), an animal model of Wilson disease, was also estimated as Zn bound to CAIII and shown to be lower than that in Wistar rats before the onset of hepatitis. The concentration of CAIII was decreased specifically by repeated injections of cupric ions without the Cu,Zn-SOD concentration being affected.     

Immunoelectron microscopic localization of carbonic anhydrase III in rat skeletal muscle

Summary The subcellular distribution of carbonic anhydrase III in rat soleus and vastus lateralis muscles was studied using an immunogold technique. The enzyme protein was found to be distributed diffusely in the cytoplasm of skeletal muscle cells. Red skeletal muscle (mainly type I fibers) revealed very strong immunogold staining whereas in white muscle (mainly type II fibers) gold particles were almost completely absent. No immunoreaction was observed in mitochondria or in other intracellular organelles.     

Determination and developmental changes in carbonic anhydrase III in swine liver.

1. CA-III was measured by enzyme-immunoassay in the livers of male and female swine aged from the fetus to 5 years old. 2. No sexual dimorphism in porcine liver could be detected at 6 months, but stag showed twice as much as swine of the same age. 3. The concentration of CA-III in the liver increased during development up to 6 months of age, followed by decline due to senescence.     

Synthesis of rat muscle carbonic anhydrase III in a cell-free translation system

Carbonic anhydrase III (CA III) was identified in the products of rat soleus muscle RNA translation in vitro by both a radioimmunoassay and a specific immunoprecipitation technique followed by SDS--polyacrylamide gel electrophoresis analysis of the precipitated antigen. The primary translation product has the same Mr-value as the native isoenzyme. CA III mRNA was found to represent approximately 0.55% of the total mRNA present in rat soleus muscle.     

Hormonal manipulation and neonatal imprinting of carbonic anhydrase isozymes in rat liver

Thyroidectomy has a feminizing effect on the carbonic anhydrase isozymes II and III in male rat liver. These isozymes are known to be sexually differentiated but no treatment so far administered has produced total feminization and this is also true for thyroidectomy. Neonatal castration, however, does produce this result, suggesting the possibility of androgen imprinting for these isozymes during the neonatal period.     

Novel purification of carbonic anhydrase III from human, rat and baboon muscle

A new method of inhibitor elution from DEAE cellulose is described for carbonic anhydrase III. Highly purified fractions free of other isozymes were obtained after one column elution.     

Identification of an abundant S-thiolated rat liver protein as carbonic anhydrase III; characterization of S-thiolation and dethiolation reactions

An S-thiolated 30-kDa protein has been purified from rat liver by two steps of ion-exchange chromatography. This monomeric protein has two "reactive" sulfhydryls that can be S-thiolated by glutathione (form a mixed disulfide with glutathione) in intact liver. The protein has been identified as carbonic anhydrase III by sequence analysis of tryptic peptides from the pure protein. The two "reactive" sulfhydryls on this protein can produce three different S-thiolated forms of the protein that can be separated by isoelectric focusing. Using this technique it was possible to study the S-thiolation and dethiolation reactions of the pure protein. The reduced form of this protein was S-thiolated both by thiol-disulfide exchange with glutathione disulfide and by oxyradical-initiated S-thiolation with reduced glutathione. The S-thiolation rate of this 30-kDa protein was somewhat slower than that of glycogen phosphorylase b by both S-thiolation mechanisms. The S-thiolated form of this protein was poorly dethiolated (i.e., reduced) by glutathione, cysteine, cysteamine, or coenzyme A alone. Enzymatic catalysis by two different enzymes (glutaredoxin and thioredoxin-like) greatly enhanced the dethiolation rate. These experiments suggest that carbonic anhydrase III is a major participant in the liver response to oxidative stress, and that the protein may be S-thiolated by two different non-enzymatic mechanisms and dethiolated by enzymatic reactions in intact cells. Thus, the S-thiolation/dethiolation of carbonic anhydrase III resembles glycogen phosphorylase and not creatine kinase.     

Thyroidectomy significantly alters carbonic anhydrase III concentration and fiber distribution in rat muscle

Thyroidectomy has a dramatic effect on rat muscle, greatly increasing the number of Type I fibers and the concentrations of carbonic anhydrase III (CAIII) in the muscle. Carbonic anhydrase III is not confined to the Type I fibers, as was previously believed, but also occurs in fibers that exhibit a level of ATPase staining less than that of 2A fibers but greater than 2B. These fibers are rare in normal muscle but become numerous after thyroidectomy, when they stain heavily for CAIII.     

Some properties of site-specific mutants of human carbonic anhydrase II having active-site residues characterizing carbonic anhydrase III

Four amino acid residues, His64, Asn67, Leu198 and Val207, in the active site of human carbonic anhydrase II, have been replaced by Lys64, Arg67, Phe198 and Ile207, which are characteristic for the muscle-specific, low-activity isoenzyme form, carbonic anhydrase III. The aim of the investigation has been to test if any of these residues, or a combination of them, is important for the low CO2 hydration activity, low esterase activity, low pKa for the pH/rate profile and low affinity for sulfonamide inhibitors characterizing carbonic anhydrases III. However, no evidence for such critical roles was found. A combination of Lys64 and Arg67 appears to result in a decrease in CO2 hydration activity, but even the quadruple mutant having all four changes is only eight times less active (kcat/Km) than unmodified isoenzyme II, in contrast to isoenzyme III which is nearly 300 times less active than isoenzyme II. The 4-nitrophenyl acetate hydrolase activity of the quadruple mutant is sevenfold lower than that of unmodified isoenzyme II, while the active site of isoenzyme III hardly catalyzes the hydrolysis of this ester at all. The pKa controlling the esterase activity of the quadruple mutant is 6.2, which should be compared to a value of 6.8 for unmodified isoenzyme II, and about 5 for isoenzyme III. While isoenzyme III binds sulfonamide inhibitors 10(3)-10(4) times less strongly than isoenzyme II, only [Asn-67----Arg]isoenzyme II shows a weaker binding of the investigated sulfonamide, dansylamide, but only by a factor of two. Some of the other mutants show enhanced affinities, up to nearly fourfold for the double mutant with Phe198 and Ile207. It is speculated that additional differences between the active sites of isoenzyme II and III might be important for the precise orientations and interactions of the side chains of isoenzyme-III-specific amino acid residues.     

Purification and properties of pig muscle carbonic anhydrase III

Pig muscle carbonic anhydrase III (carbonate hydro-lyase, EC 4.2.1.1) has been isolated and purified to homogeneity with chromatographic techniques. It has been found to be a 30 kDa protein displaying the same three activities (CO2 hydratase, acetate esterase, p-nitrophenyl phosphatase) previously described for the rabbit muscle isoenzyme, including the phosphatase activity not seen in the erythrocyte isoenzymes. The turnover numbers of the three activities are of the same order of magnitude as previously reported for rabbit muscle carbonic anhydrase III. Km and Vmax for the pig muscle CO2 hydratase activity were found to be 83 mM and 6000 s-1, respectively. The extinction coefficient at 280 nm (1 cm light path) is 22.2 for a 1% solution. Five half-cystine residues determined by performic acid oxidation are free for reaction with p-mercuribenzoate but only four are accessible to titration with dithiobisnitrobenzene. The amino acid composition of the pig muscle isoenzyme III has a high level of homology compared with that of rabbit and bovine muscle carbonic anhydrases III.     

Characterization of human carbonic anhydrase III from skeletal muscle

A third form of human carbonic anhydrase (CA III), found at high concentrations in skeletal muscle, has been purified and characterized. This isozyme shows relatively poor hydratase and esterase activities compared to the red cell isozymes, CA I and CA II, but is similar to these isozymes in subunit structure (monomer) and molecular size (28,000). CA III is liable to posttranslational modification by thiol group interaction. Monomeric secondary isozymes, sensitive to beta-mercaptoethanol, are found in both crude and purified material and can be generated in vitro by the addition of thiol reagents. Active dimeric isozymes, generated apparently by the formation of intermolecular disulfide bridges, also occur but account for only a small proportion of the total protein and appear only when the concentration of CA III is particularly high.     

Localization of carbonic anhydrase in the rat lung

Summary The localization of carbonic anhydrase in the rat lung has been demonstrated, at light and electron microscopic levels, by the cobalt bicarbonate histochemical method of Hansson. Focal deposits of the cobalt sulfide reaction product were found not only in the capillary endothelium of the alveolar walls, but also in the small and large alveolar cells. The histochemical reaction was abolished by two potent inhibitors, acetazolamide (10^–5 to 10^–6 M) and KCNO (5×10^–3 to 10×10^–3 M). Physiological assay with Maren's method indicated that values for carbonic anhydrase activity in rat lung are 4.4±0.8 UA/mg of protein, 25.0±5.5 UA/mg of nitrogen, and 369±86 UA/g of wet weight. In addition, it was calculated that after fixation in glutaraldehyde-formaldehyde-picric acid about 9% activity is retained.     

Zinc and carbonic anhydrase III distribution in mammalian muscle

Zinc and carbonic anhydrase III measurement in human and rat muscle extracts indicate that: 1. About one fifth of zinc in human soleus is associated with carbonic anhydrase III isozyme, and even higher levels of zinc and carbonic anhydrase III are found in rat soleus, where about one half of the zinc is in carbonic anhydrase III. Other muscle was also analysed in a similar way, (see text). Heart is notable in containing lower levels of zinc but negligible carbonic anhydrase III. 2. Treatment of muscle with water or phosphate solutions showed that all the carbonic anhydrase III was water extractable, whereas significant zinc remained bound, but was partially extractable by phosphate solutions. 3. Dialysis of muscle extracts showed that whilst some zinc was dialysable, there was no significant contribution from the carbonic anhydrase III in the dialysed extract. EDTA enhanced the release of dialysable zinc from muscle extract. These findings are discussed in relation to muscle disease.     

Towards a biomarker of mammalian senescence: carbonic anhydrase III

Three proteins (D2, D3, D4) have been identified in the male Fischer 344 rat liver that decrease their concentration dramatically to virtually zero during the transition from physiological maturity to senescence. D3 (Mr 28 kDa), absent (or at a very low concentration) from the livers of newborns and females of all ages, reaches at 60 days (sexual maturity) its maximum concentration, which declines almost linearly thereafter. A homologous protein (CNBr peptide map) occurs in the BALB/c mouse under similar conditions. D3 was purified and since its N-terminal is blocked, digested with CNBr. SDS-PAGE-separated peptides were blotted upon Immobilon and sequenced. The partial sequence matches that of rat carbonic anhydrase III. Treatment of senescent rats with 5 alpha-dihydrotestosterone restores D4 completely, yet D2 and D3 only partially, towards their maximum life-time concentration. Thus senescence-related factors (e.g. hepatic androgen receptor) aside from serum testosterone are responsible for the disappearance of the three proteins from the senescent liver.