Biochemical and genetic analysis of pre-stalk specific acid phosphatase in Dictyostelium

The only known enzymatic marker of pre-stalk cells at the slug stage of development in Dictyostelium discoideum is an isozyme of acid phosphatase, AP2. There is another isozyme of acid phosphatase, AP1, which is present in vegetative cells and is not cell-type specific. We have purified these isozymes and find they differ in K_m and thermostability. Both isozymes are affected by mutations in a single locus, acpA. Two mutations in the acpA locus abolished all activity of both AP1 and AP2 while a third mutation reduced the activity and altered the thermostability of both isozymes. It is likely that acpA is the structural gene responsible for both AP1 and AP2. The cell-type specificity of AP2 appears to result from differences in the modification of the acpA gene product between pre-spore and pre-stalk cells. The resulting difference in AP2 provides a useful marker for pre-stalk cells.     

Developmental changes in the modification of lysosomal enzymes in Dictyostelium discoideum

Evidence has been found for a generalized change in the post-translational modification of lysosomal enzymes during development of Dictyostelium discoideum. The physical and antigenic properties of four developmentally regulated lysosomal enzymes, N-acetylglucosaminidase, beta-glucosidase, alpha-mannosidase, and acid phosphatase, have been examined throughout the life cycle. In vegetative cells, a single major isoelectric species is detected for each enzymatic activity on native nonequilibrium isoelectric focusing gels. Between 6 and 10 hr of development, all activities, including the preformed enzyme, become less negatively charged, resulting in a modest but reproducible shift in the isoelectric focusing pattern. This alteration is not detected by native gel electrophoresis at constant pH. As development continues, the specific activity of beta-glucosidase, alpha-mannosidase, and acid phosphatase continues to increase and coincidentally, new, less acidic isozymic bands of activity can be observed on both gel systems. Some of these new isozymes accumulate preferentially in anterior cells, while others accumulate preferentially in posterior cells of migrating slugs. N-Acetylglucosaminidase does not increase in specific activity late in development and no new isozymic species appear. Using a monoclonal antibody that reacts with sulfated N-linked oligosaccharides shared by vegetative lysosomal enzymes in D. discoideum, the antigenicity of the developmental isozymes has been characterized. All of the enzymatic activity present during vegetative growth and early development is immunoprecipitable. However, the less negatively charged isozymes that accumulate after aggregation are not recognized by the antibody. Nonantigenic acid phosphatase and alpha-mannosidase are found in both anterior and posterior cells from migrating pseudoplasmodia. Since each enzyme is coded by a single structural gene, these results suggest that the isozymes present late in development arise from the synthesis of the same polypeptides with altered post-translational modifications. The appearance of anterior and posterior specific isozymes is likely to be the result of cell type specific changes in the glycoprotein modification pathway for newly synthesized proteins.     

The alpha-glucosidases of Dictyostelium discoideum. II. Developmental regulation and cellular localization

Four isozymes of α-glucosidase in Dictyostelium discoideum have been identified and some of their enzymatic and physical properties characterized (R. H. Borts and R. L. Dimond, 1981, Develop. Biol.87, 176–184). In this report the cellular localization and developmental regulation of three of these isozymes are determined. α-Glucosidase-1 is the major isozyme of vegetative amoebae. It is lysosomally localized and secreted from the cell under certain conditions. It has an acidic pH optimum and carries the common antigenic determinant found on all lysosomal enzymes in this organism. The specific activity of this isozyme begins to decrease within a few hours after the initiation of development and is no longer detectable in the mature fruiting body. α-Glucosidase-2 has a neutral pH optimum and is neither lysosomal nor secreted. Rather it is membrane bound and is possibly located on the cisternal side of microsomal vesicles. This isozyme does not possess the common antigenic determinant. α-Glucosidase-2 comprises 20–40% of the total α-glucosidase activity of the vegetative cell. Its specific activity increases threefold during development. This isozyme appears to be developmentally controlled since it fails to accumulate in aggregation deficient mutants. Its accumulation is also dependent upon continued protein synthesis. α-Glucosidase-4, like α-glucosidase-1, has an acidic pH optimum. It does not appear to be lysosomally localized nor membrane bound. Approximately 30% of the activity is precipitable by antibody against the common antigenic determinant indicating that it is less highly modified or fewer molecules are modified. The isozyme is undetectable during vegetative growth and does not begin to accumulate until late aggregation. Activity peaks in mature fruiting bodies where it is the predominant acidic α-glucosidase activity. Accumulation of α-glucosidase-4 is blocked in morphologically deficient mutants and by inhibitors of protein synthesis.     

A late developmental change in lysosomal enzyme sulfation specific to newly synthesized proteins in Dictyostelium discoideum

During development in Dictyostelium discoideum, several lysosomal glycosidases undergo changes in post-translational modification that are thought to involve differences in the extent of sulfation or phosphorylation, and appear to be required for the maintenance of cellular enzyme activity late in development. We have used monoclonal antibodies specific to the lysosomal enzyme alpha-mannosidase-1 to study the major late (12 hr) developmental change in the modification system. Pulse-chase experiments performed both early and late in development reveal that the substrate for the late form of modification is restricted to newly synthesized alpha-mannosidase-1 precursor protein. We have identified one modification difference between the two developmentally distinct isozymes of alpha-mannosidase-1: 35SO4 pulse-chase data show that the newly synthesized "late" enzyme precursor is significantly undersulfated in comparison with the enzyme synthesized early in development. This apparent lack of sulfation is associated with the lack of acquisition of endoglycosidase H resistance. By contrast, an aggregation-deficient mutant, which is defective with regard to the accumulation of alpha-mannosidase-1 activity late in development, synthesizes the "early" sulfated form of the enzyme throughout development. We conclude that the late developmental change in post-translational modification specifically involves one of the biochemical steps in which the N-linked oligosaccharide side chains of the newly synthesized alpha-mannosidase-1 precursor are modified by sulfation.     

Three isozymes of catechol 1,2-dioxygenase (pyrocatechase), alpha alpha, alpha beta, and beta beta, from Pseudomonas arvilla C-1

Three isozymes of catechol 1,2-dioxygenase (pyrocatechase) from Pseudomonas arvilla C-1 were separated using DEAE-Toyopearl chromatography. The specific activities of each isozyme were similar to one another. The molecular weights of isozymes 1, 2, and 3 were estimated to be approximately 67,000, 64,000, and 59,000, respectively, from gel filtration. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, isozymes 1 and 3 gave a single protein band, corresponding to Mr = 32,000 and 30,000, respectively, and isozyme 2 gave two bands corresponding to Mr = 32,000 and 30,000. These results indicated that isozymes 1 and 3 were homodimers, while isozyme 2 was a heterodimer. The NH2-terminal sequences up to 20 residues of these three isozymes confirmed that isozymes 1, 2, and 3 consisted of beta beta, alpha beta, and alpha alpha, respectively, based on our previous data (Nakai, C., Kagamiyama, H., Saeki, Y., and Nozaki, M. (1979) Arch. Biochem. Biophys. 195, 12-22). Properties of these isozymes such as absorption spectrum, iron content, substrate specificity, and kinetic constants were similar to one another. Subunit exchange between the different isozymes and dissociation of the isozymes into subunits was not observed under nondenaturing conditions. Available evidence indicates that these isozymes exist naturally in the bacterium and were not due to artifacts caused by purification.     

The requirement for DIF for prestalk and stalk cell formation in Dictyostelium discoideum: a comparison of in vivo and in vitro differentiation conditions

In Dictyostelium discoideum stalk cell formation is induced by cyclic AMP and differentiation-inducing factor (DIF) when cells are plated in in vitro monolayers (Kay et al., 1979, Differentiation 13: 7-14). The in vivo developmental stages at which cells became independent of these factors were determined. Independence was defined as the stage at which dispersed cells no longer required the factors for stalk cell formation in low density monolayers. Cyclic AMP independent cells were first detected at around 12 hr of development, a time that corresponds to the transition between the tipped aggregate and the first finger stages. In contrast cells did not become independent of DIF until late culmination. The prestalk cell-specific isozyme acid phosphatase II and a stalk cell-specific 41,000 Mr antigen (ST 41) were expressed during differentiation in low density monolayers in the presence of both cyclic AMP and DIF, but neither component was expressed in the presence of cyclic AMP alone. This result implies that DIF is essential for both prestalk and stalk cell formation. The two components were expressed within 2 hr of each other during differentiation in vitro, whereas during development in vivo acid phosphatase II was first detected at the first finger stage and ST 41 was first detected during late culmination, 8-12 hr later. These contrasting results suggest that the conversion of prestalk cells to stalk cells is unrestrained in monolayers, following directly after prestalk cell induction, but restrained in vivo until the culmination stage. This interpretation is consistent with the finding that cells become independent of DIF early during in vitro differentiation (A. Sobolewski, N. Neave, and G. Weeks, 1983, Differentiation 25, 93-100), but do not become independent of DIF until the culmination stage when differentiating in vivo.     

Calmodulin and Ca2+-dependent phosphorylation and dephosphorylation of 63-kDa subunit-containing bovine brain calmodulin-stimulated cyclic nucleotide phosphodiesterase isozyme

Bovine brain contains calmodulin-dependent cyclic nucleotide phosphodiesterase isozymes which are composed of two distinct subunits: Mr 60,000 and 63,000. The 60-kDa but not the 63-kDa subunit-containing isozyme can be phosphorylated by cAMP-dependent protein kinase resulting in decreased affinity of this subunit toward calmodulin (Sharma, R. K., and Wang, J. H. (1985) Proc. Natl. Acad. Sci. U. S. A. 82, 2603-2607). In contrast, purified 63-kDa subunit-containing isozyme has been found to be phosphorylated by a preparation of bovine brain calmodulin-binding proteins in the presence of Ca2+ and calmodulin. The phosphorylation resulted in the maximal incorporation of 2 mol of phosphate/mol of the phosphodiesterase subunit with a 50% decrease in the enzyme affinity toward calmodulin. At a constant calmodulin concentration of 6 nM, the phosphorylated isozyme required a higher concentration of Ca2+ for activation than the nonphosphorylated phosphodiesterase. The Ca2+ concentrations at 50% activation by calmodulin of the nonphosphorylated and phosphorylated isozymes were 1.1 and 1.9 microM, respectively. Phosphorylation can be reversed by the calmodulin-dependent phosphatase, calcineurin, but not by phosphoprotein phosphatase 1. The results suggest that the Ca2+ sensitivities of brain calmodulin-dependent cyclic nucleotide phosphodiesterase isozymes can be modulated by protein phosphorylation and dephosphorylation mechanisms in response to different second messengers.     

Molecular cloning of complementary DNA encoding one of the human pancreatic protease E isozymes

We have cloned a DNA from a human pancreatic cDNA library using a cloned rat pancreatic elastase 1 cDNA as a probe, and determined its nucleotide sequence. This cDNA contains a coding region of 810 nucleotides which encodes a 270-amino-acid protein. The deduced amino acid sequence shows less than 60% homologies with rat and porcine pancreatic elastase 1, although its substrate binding region is homologous with those of the above elastases 1. When this deduced amino acid sequence was compared with known amino acid sequences of pancreatic proteases other than elastases, it was found to contain an amino acid sequence which was highly homologous with the N-terminal amino acid sequence of porcine pancreatic protease E. We also purified human pancreatic protease E isozymes from human pancreatic juice, and determined their N-terminal amino acid sequences. One of the isozymes does not hydrolyze elastin but does hydrolyze a synthetic substrate. Endoglycosidase F digests glycoside bonds of the isozyme. These results suggest that the cDNA cloned by us corresponded to one of the human protease E isozymes.     

Total protein and isozyme characterization in the flax zygotic embryo during development

Flax zygotic embryogenesis was studied for isozyme patterns of acid phosphatase and esterase and for content of total proteins. For acid phosphatase, six multiple molecular forms or isozymes, were identified during flax zygotic embryo development. For esterase, six isozymes were expressed during zygotic flax embryogenesis. Some of the isozymes were expressed during entire embryogenesis, and some were only transiently expressed or appeared near maturation. The amount of total proteins was very low at early embryogenesis and proteins in a range from 26.6 kDa to 97.4 kDa were expressed. During further flax embryo development the protein spectra became more diverse and the quantity of total proteins increased. Proteins ranging from 3.4 kDa to 97.4 kDa were present, and proteins of 20 kDa to 36.5 kDa were expressed in the highest amount. The results are discussed with reference to selected information in the literature. Received: 16 October 2000 / Revision accepted: 20 April 2001     

Cathepsin D isozymes from porcine spleens. Large scale purification and polypeptide chain arrangements.

Six cathepsin D isozymes have been purified from porcine spleen using a large scale purification procedure. Five isozymes, I to V, have an identical molecular weight of 50,000 and are similar in specific activity. Isozymes I to IV contained two polypeptide chains each. The light and heavy chains have Mr = 15,000 and 35,000, respectively. Isozyme V is a single polypeptide. The molecular weight of the sixth isozyme is about 100,000 and it has only 5% of the specific activity of the other isozymes. On Ouchterlony immunodiffusion, an antiserum formed precipitin lines against the urea-denatured isozyme with Mr = 100,000. This immunoreactivity showed immunoidentity with those formed against other isozymes. The NH2-terminal sequence of light chains was identical for the isozymes. This sequence is homologous to the NH2-terminal sequence of other acid proteases, especially near the region of the active center aspartate-32. The NH2-terminal sequence of the single chain, isozyme V, Is apparently the same as the light chain sequence. The NH2-terminal sequence analysis of the heavy chain from isozyme I produced two sets of related sequences, suggesting the prescene of structural microheterogeneity. The carbohydrate analysis of the isozymes, the light chain, and the heavy chain revealed the presence of possibly four attachment sites, with one in the light chain and three in the heavy chain. Each carbohydrate unit contains 2 residues of mannose and 1 residue of glucosamine. The results suggest that the high molecular weight cathepsin D (Mr = 100,000) is the probable precursor of the single chain (Mr = 50,000), which in turn produces the two-chain isozymes. These are likely in vivo processes.     

Comparison of the property of a novel isozyme E (formerly null mutant, O) with other isozymes of hemolymph acid phosphatase of the silkworm

1. A novel acid phosphatase isozyme E (formerly null mutant 0) was partially purified by ammonium sulfate fractionation, DEAE-Sephacel and Sephacryl S-200 column chromatography, and its properties were compared with those of other isozymes of the silkworm hemolymph. 2. The isozyme E was extremely heat labile and showed lower pH-stability than those of others. 3. Three isozymes hydrolyzed p-nitrophenyl phosphate, alpha-naphthyl phosphate, alpha-naphthyl phosphate and glucose-1-phosphate strongly. The isozyme E showed about 50% hydrolyzing activity for alpha-naphthyl phosphate as compared to those of A and B. 4. Activities of three isozymes were inhibited by tartaric acid, sodium fluoride, ammonium molybdate and potassium diphosphate. Inhibitory effects of Cu(2+) and HG(2+) were most remarkable against E isozyme.     

Characterization and developmental regulation of beta-galactosidase isozymes in Dictyostelium discoideum.

Two isozymes of β-galactosidase (EC 3.2.1.23) have been identified during growth and development of the cellular slime mold, Dictyostelium discoideum. The isozymes have been partially purified and differ in a variety of physical and enzymatic properties. β-Galactosidase-1 is present in vegetative cells. The specific activity is reduced during early development and then increases again during culmination. The specific activity of β-galactosidase-2 increases in early development and then again during culmination and spore maturation. The specific activity of β-galactosidase-2 is extremely dependent upon growth conditions and is regulated over a 160-fold range. The accumulation of both isozymes is dependent on concomitant RNA and protein synthesis.     

Electrophoretic characterization of six selected enzymes of peanut cultivars

The isozyme patterns (both anodic and cathodic) of esterase, catalase, leucine aminopeptidase, acid phosphatase, alcohol dehydrogenase and INT oxidase in individual seeds from several peanut cultivars (Arachis hypogaea) were characterized by polyacrylamide and starch gel electrophoresis in relation to the stages of seed development, maturity, and germination, geographic areas where grown and phylogenetic relationship. Of the six enzymes examined, only esterase contained cathodic isozymes, of which the patterns served to distinguish between the Spanish and the Virginia-type peanuts. Anodic esterase and acid phosphatase zymograms of early developing and germinating peanuts could be distinguished from those of predormant and mature seeds and the latter showed much intravarietal variation which was consistent among cultivars and the geographic areas where grown. Anodic isozymes of catalase, leucine aminopeptidase, alcohol dehydrogenase and INT oxidase were synthesized very early in peanut development and remained constant through maturity and to at least 24 hr germination; they were consistent within and between peanut cultivars and they were not influenced by the environmental conditions of the areas where the peanuts were grown. The consistency of the isozyme patterns within and between cultivars supports the suggestion that plant breeding programs used to develop superior cultivars have produced genetic uniformity in peanuts.     

Identification and partial characterization of bovine heart cytosolic phosphorylase phosphatases

The properties of phosphatases in bovine heart cytosol were studied. Two isozymic forms of protein phosphatase H (H-1 and H-2) were resolved by chromatography on DEAE-Sephacel. The two isoenzymes had identical physical properties (Mr 260,000, 7.9 S). Treatment with 80% ethanol activated both isozymes and converted H-1 to a Mr 35,500 form and H-2 to Mr 67,000 and Mr 35,500 forms. Both H-1 and H-2 and their lower Mr activated forms had essentially identical Km values for phosphorylase a. The heart cytosol also contained a latent phosphatase (Fc) which could be activated by preincubation with either ATP X Mg and an activating factor (FA), or by Mn/trypsin treatment. The latter procedure converted the latent Fc (Mr 200,000) to a Mn2+-independent Mr 34,500 form. Both activated forms of Fc had similar Km values which were fourfold lower than the affinity of the protein phosphatase H forms for the phosphorylase a substrate.     

Isozymes of isocitrate dehydrogenase from an obligately psychrophilic bacterium, Vibrio sp. strain ABE-1: purification, and modulation of activities by growth conditions

Each of the two isozymes, which are different in thermostability and quaternary structure, of isocitrate dehydrogenase (NADP+) [IDH: EC 1.1.1.42] was purified to an electrophoretically homogeneous state from an obligately psychrophilic marine bacterium, Vibrio sp. strain ABE-1. Hydrophobic chromatography was an efficient procedure to separate the two isozymes from each other. The isoelectric points of isozyme I (IDH-I; a dimer, Mr 88,100) and isozyme II (IDH-II; a monomer, Mr 80,500) were found to be pH 4.9 and 5.2, respectively. The two isozymes were similar in amino acid compositions, though there were slight differences in the contents of nonpolar and hydroxyl amino acids. However, their NH2-terminal amino acid sequences and immunochemical properties were clearly different from each other. The NH2-terminal amino acid sequence analysis also indicated that the subunits of IDH-I are chemically identical or highly homologous. Non-immuno-crossreactivity between the isozymes enabled us to measure the intracellular contents of the isozymes. IDH-I and -II were found to be differentially regulated in vivo by various growth conditions. IDH-I was induced by acetate, while IDH-II remained almost unchanged.     

Structure and function of beta-blucosidases in Dictyostelium discoideum.

There are two isozymes of beta-glucosidase in developing cells of Dictyostelium discoideum. A procedure for screening large numbers of clones for beta-glucosidase activity was utilized to obtain mutations which directly affect the activity. We recovered seven strains which lack both isozymes and four strains with residual activity in which enzymatic and physical properties of both isozymes are altered. Beta-Glucosidase appears to act as a block to selfing in macrocyst formation as shown by the fact that ssite mating type to form macrocyst-like structures. Immunological evidence utilizing antisera prepared against purified beta-glucosidase-1 demonstrates that most of the glycosidases in Dictyostelium discoideum share a common antigenic determinant which appears to be added post-translationally. The two isozymes of beta-glucosidase share common protein subunits but the antigenic determinant is either lacking or masked in beta-glucosidase-2. This may account for some of the enzymatic and physical differences between the two isozymes.     

Expression of the alpha, beta II, and gamma protein kinase C isozymes in the baculovirus-insect cell expression system. Purification and characterization of the individual isoforms

Detailed in vitro comparisons of the biochemical characteristics of three protein kinase C isozymes were performed. As an alternative to earlier uncertain separation methods and expression schemes, highly purified and genetically distinct protein kinase C enzymes were produced using the baculovirus expression system. The baculovirus expression system yielded approximately 200-300 micrograms of the purified isozyme from 3 x 10(8) (100 ml of culture medium) baculovirus-infected insect cells. Biochemical characterization of the expressed isozymes indicated that the three isozymes had virtually indistinguishable Ca2+, Mg2+, and ATP dependencies. However, in certain critical functional characteristics such as phosphatidylserine dependencies, phospholipid and substrate preferences, and arachidonic acid activation, the gamma isozyme exhibited distinctive properties when compared with both the alpha and beta II subtypes. In addition, the activity of the beta II subtype was more dependent upon diacylglycerol or phorbol esters for activation than either the alpha or gamma isoforms. The alpha isozyme, unlike the beta II and gamma forms, was totally dependent on Ca2+ for activation in the presence of free arachidonic acid. These studies provide definitive characterizations of the pure isoforms; many of the findings were consistent with earlier enzymatic observations using hydroxyapatite-purified isoforms. Thus, the distinctive biochemical properties of the protein kinase C isozymes are consistent with the hypothesis that each isoform may have distinct roles in signal transduction processes.     

Purification and characterization of laccase isozymes from the white-rot basidiomycete Ganoderma lucidum

Ganoderma lucidum, a medicinal white-rot basidiomycete, produces many laccase isozymes in liquid culture. Three laccase isozymes (GaLc 1, 2, 3) have been purified 32.4-fold from the crude enzyme protein through anion exchange chromatography, preparative gel electrophoresis, and electroelution. Their estimated molecular weights are 65-68 kDa, and they contain 7-10% N-linked carbohydrates. The three isozymes have identical N-terminal amino acid sequences: G-I-G-P-T. The optimum pH and temperature both for each isozyme singly and the isozyme mixture are pH 3.5 and 20 degrees C, respectively. One isozyme (GaLc 3) is quite stable at pH 4.0-10.0, and shows good stability when incubated at temperatures lower than 40 degrees C. The Km values of GaLc 3 for o-tolidine and 2,2'-azino-bis-(3-ethylthiazoline-6-sulfonate) (ABTS) are 401.6 microM and 3.7 microM respectively, and the Vmax of GaLc 3 for these substrates is 0.0198 OD min(-1) unit(-1) and 0.0142 OD min(-1) unit(-1), respectively.     

Horse liver aldehyde dehydrogenase. Purification and characterization of two isozymes.

Two isozymes of horse liver aldehyde dehydrogenase (aldehyde, NAD oxidoreductase (EC 1.2.1.3)), F1 and F2, have been purified to homogeneity using salt fractionation followed by ion exchange and gel filtration chromatography. The specific activities of the two isozymes in a pH 9.0 system with propionaldehyde as substrate were approximately 0.35 and 1.0 mumol of NADH/min/mg of protein for the F1 and F2 isozymes, respectively. The multiporosity polyacrylamide gel electrophoresis molecular weights of the F1 and F2 isozymes were approximately 230,000 and 240,000 respectively. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis gave subunit molecular weight estimates of 52,000 and 53,000 for the F1 and F2 isozymes, respectively. The amino acid compositions of the two isozymes were found to be similar; the ionizable amino acid contents being consistent with the electrophoretic and chromatographic behavior of the two isozymes. Both isozymes exhibited a broad aldehyde specificity, oxidizing a wide variety of aliphatic and aromatic aldehydes and utilized NAD as coenzyme, but at approximately 300-fold higher coenzyme concentration could use NADP. The F1 isozyme exhibited a very low Km for NAD (3 muM) and a higher Km for acetaldehyde (70 muM), while the F2 isozyme was found to have a higher Km for NAD (30 muM) and a low Km for acetaldehyde (0.2 muM). The two isozymes showed similar chloral hydrate and p-chloromercuribenzoate inhibition characteristics, but the F1 isozyme was found to be several orders of magnittude more sensitive to disulfiram, a physiological inhibitor of acetaldehyde oxidation. Based on its disulfiram inhibition characteristics, it has been suggested that the F1 isozyme may be the primary enzyme for oxidizing the acetyldehyde produced during ethanol oxidation in vivo.     

Differential expression of alpha, mu and pi classes of isozymes of glutathione S-transferase in bovine lens, cornea, and retina

Isozyme characterization of glutathione S-transferase (GST) isolated from bovine ocular tissue was undertaken. Two isozymes of lens, GST 7.4 and GST 5.6, were isolated and found to be homodimers of a Mr 23,500 subunit. Amino acid sequence analysis of a 20-residue region of the amino terminus was identical for both isozymes and was identical to GST psi and GST mu of human liver. Antibodies raised against GST psi cross-reacted with both lens isozymes. Although lens GST 5.6 and GST 7.4 demonstrated chemical and immunological relatedness, they were distinctly different as evidenced by their pI and comparative peptide fingerprint. A corneal isozyme, GST 7.2, was also isolated and established to be a homodimer of Mr 24,500 subunits. Sequence analysis of the amino-terminal region indicated it to be about 67% identical with the GST pi isozyme of human placenta. Antibodies raised against GST pi cross-reacted with cornea GST 7.2. Another corneal isozyme, GST 8.7, was found to be homodimer of Mr 27,000 subunits. Sequence analysis revealed it to have a blocked amino-terminus. GST 8.7 immunologically cross-reacted with the antibodies raised against cationic isozymes of human liver indicating it to be of the alpha class. Two isozymes of retina, GST 6.8 and GST 6.3, were isolated and identified to be heterodimers of subunits of Mr 23,500 and 24,500. Amino-terminal sequence analysis gave identical results for both retina GST 6.8 and GST 6.3. The sequence analysis of the Mr 23,500 subunit was identical to that obtained for lens GSTs. Similarly, sequence analysis of the Mr 24,500 subunit was identical to that obtained for the cornea GST 7.2 isozyme. Both the retina isozymes cross-reacted with antibodies raised against human GST psi as well as GST pi. The results of these studies indicated that all three major classes of GST isozymes were expressed in bovine eye but the GST genes were differentially expressed in lens, cornea, and retina. In lens only the mu class of GST was expressed, whereas cornea expressed alpha and pi classes and retina expressed mu and pi classes of GST isozymes.