Aspartate Aminotransferase Isoenzymes Research Articles

Distributions of the activities of aspartate aminotransferase isoenzymes in rat retinal layers.

Distributions of the activities of the cytosolic (cAAT) and mitochondrial (mAAT) isoenzymes of aspartate aminotransferase were determined in rat retinal layers. cAAT was highest in the photoreceptor inner segments, inner nuclear layer and inner plexiform layer; mAAT was highest in the inner segments. The high activity in the inner segments indicates that both isoenzymes are involved in energy metabolism in addition to a possible role in neurotransmission.

Quantitation of aspartate aminotransferase isoenzymes after electrophoretic separation

A scheme for the quantitative detection of aspartate aminotransferase isoenzymes and multiple forms after electrophoretic separation is described. Glutamate generated from the aminotransferase reaction is quantitated by using the glutamate dehydrogenase/diaphorase-coupled enzyme system to form a formazan dye. Product inhibition of aspartate aminotransferase by oxaloacetate is prevented by including oxaloacetate decarboxylase in the overlay reagent. Results compare favorably with those of an immunochemical precipitation procedure. The method can also be used to detect quantitatively subforms and atypical forms (genetic variants, immunoglobulin-enzyme complexes) of aspartate aminotransferase.

Activity of serum aspartate aminotransferase isoenzymes in patients with acute myocardial infarction.

Activities of aspartate aminotransferase (AST) isoenzymes were determined in serial serum samples from 40 cases of acute myocardial infarction, and compared with activities of creatine kinase, CK-MB isoenzyme, lactate dehydrogenase, and alpha-hydroxybutyrate dehydrogenase for temporal changes. Cytosolic (soluble) AST (s-AST) and mitochondrial AST (m-AST) respectively increased 6.6 and 9.0 h after onset of chest pain. The median time at which serum m-AST activity peaked (15.8 U/L, range 6.4-53.5 U/L) was 47.8 h after the onset of infarction, 19.8 h later than the peak s-AST activity (171 U/L, range 53-517 U/L) and m-AST also disappeared from the serum more slowly than s-AST (p less than 0.001). Serum m-AST values were above normal for at least six days after the infarct. The ratio of m-AST to total AST in serum increased after myocardial infarction, being greatest (20%, range 11-32%) on the third day after onset. For individuals, peak activities of s-AST correlated well with total CK (r = 0.91) and CK-MB (r = 0.86) peak activities, indicating that s-AST also reflects the infarct size. However, m-AST correlated poorly with the enzymes commonly used in infarct diagnosis; it apparently provides different biological information.

A kinetic method for quantification of aspartate aminotransferase isoenzymes

A spectrophotometric assay is proposed to determine the levels of aspartate aminotransferase (AAT) isoenzymes from chicken liver by a steady-state kinetic method which depends on the differential inhibition of these isoenzyme forms by high concentrations of substrate 2-oxoglutarate at pH 6.2. The use of a standard curve permits the determination of the percentage of chicken liver c-AAT and m-AAT isoenzymes. This method yields results in good correlation with those achieved by different extent adipate inhibition and by differential centrifugation.

Cloning and sequence analysis of mRNA for mouse aspartate aminotransferase isoenzymes.

The nucleotide sequences of mRNAs for the mouse mitochondrial and cytosolic aspartate aminotransferase isoenzymes (mAspAT and cAspAT) (EC 2.6.1.1) were determined from complementary DNAs. The mAspAT mRNA comprises minimally 2460 nucleotides and codes for a polypeptide of 430 amino acid residues corresponding to the precursor form of the mAspAT (pre-mAspAT). The cAspAT mRNA comprises minimally 2086 nucleotides and codes for a polypeptide of 413 amino acid residues. The region coding for the mature mAspAT and that for the cAspAT show about 53% overall homology. The former shares 49% and the latter 48% of homology, respectively, with that of the Escherichia coli aspC gene, which has been shown to code for the E. coli AspAT (Kuramitsu, S., Okuno, S., Ogawa, T., Ogawa, H., and Kagamiyama, H. (1985) J. Biochem. (Tokyo) 97, 1259-1262). When the deduced amino acid sequence of the mouse pre-mAspAT was compared with that of the pig pre-mAspAT polypeptide, we found that they share a 94% homology and that the mouse pre-mAspAT yields a presequence consisting of 29 amino acid residues and a mature mAspAT, consisting of 401 amino acid residues. These numbers and the amino acid residues present at the putative cleavage site are all in complete agreement in these two species. The deduced amino acid sequence of the mouse cAspAT shares 91% homology with that of the pig cAspAT. Comparisons of the nucleotide and deduced amino acid sequences between the mouse and E. coli AspATs suggest that the mammalian mAspAT gene is more closely related to the E. coli aspC gene than is the mammalian cAspAT gene.

The cloning and sequence analysis of the aspC and tyrB genes from Escherichia coli K12. Comparison of the primary structures of the aspartate aminotransferase and aromatic aminotransferase of E. coli with those of the pig aspartate aminotransferase isoenzymes.

In this paper we describe the cloning and sequence analysis of the tyrB and aspC genes from Escherichia coli K12, which encode the aromatic aminotransferase and aspartate aminotransferase respectively. The tyrB gene was isolated from a cosmid carrying the nearby dnaB gene, identified by its ability to complement a dnaB lesion. Deletion and linker insertion analysis located the tyrB gene to a 1.7-kilobase NruI-HindIII-digest fragment. Sequence analysis revealed a gene encoding a 43 000 Da polypeptide. The gene starts with a GTG codon and is closely followed by a structure resembling a rho independent terminator. The aspC gene was cloned by screening gene banks, prepared from a prototrophic E. coli K12 strain, for plasmids able to complement the aspC tyrB lesions in the aminotransferase-deficient strain HW225. Sub-cloning and deletion analysis located the aspC gene on a 1.8-kilobase HincII-StuI-digest fragment. Sequence analysis revealed the presence of a gene encoding a 43 000 Da protein, the sequence of which is identical with that previously obtained for the aspartate aminotransferase from E. coli B. Considerable overproduction of the two enzymes was demonstrated. We compared the deduced protein sequences with those of the pig mitochondrial and cytoplasmic aspartate aminotransferases. From the extensive homology observed we are able to propose that the two E. coli enzymes possess subunit structures, subunit interactions and coenzyme-binding and substrate-binding sites that are very similar both to each other and to those of the mammalian enzymes and therefore must also have very similar catalytic mechanisms. Comparison of the aspC and tyrB gene sequences reveals that they appear to have diverged as much as is possible within the constraints of functionality and codon usage.

Changes in mass and catalytic activity concentrations of aspartate aminotransferase isoenzymes in serum after a myocardial infarction.

We used an RIA and inhibition of enzyme activity to monitor the changes in mass and catalytic concentrations of the aspartate aminotransferase (EC 2.6.1.1;AST) isoenzymes in serum after myocardial infarction. Cytosolic (c-AST) and mitochondrial (m-AST) forms of AST were present in sera from all 38 of our patients. Although the immunological and catalytic concentrations of both isoenzymes correlated well with the size of the infarct, c-AST gave a better measure than did m-AST. About 20% of the total enzyme activity at peak activity was from the mitochondrial isoenzyme. Both isoenzyme activities peak at very nearly the same time, but m-AST has the longer half-life. Immunological evidence of the mitochondrial isoenzyme can be detected in serum for at least eight days after the infarct. The presence of left ventricular failure produces greater serum isoenzyme activities than in those without failure.

Lipid peroxidation in neonatal rat heart cell cultures: effects of cumene hydroperoxide

In this study neonatal rat heart cell cultures were evaluated on their potential merit for studying the oxidative component in the cardiotoxic action of drugs. Cumene hydroperoxide was used as a model compound. Cumene hydroperoxide induced enzyme release from the myocyte cultures which appeared to be both dose- and substrate(glucose)-dependent. Significant correlations were found between depletion of GSH and increased GSSG formation on the one hand and enzyme release on the other hand. Furthermore the formation of malondialdehyde, one of the products of lipid peroxidation, was measured, which correlated with enzyme release as well. Measurements on the release of the mitochondrial isoenzyme of aspartate aminotransferase imply that the lipid peroxidative process affects primarily the sarcolemmal membrane. The results indicate that myocytes in culture can provide a convenient in vitro system to assess the peroxidative action of cardiotoxic agents.

The primary structure of the precursor of chicken mitochondrial aspartate aminotransferase. Cloning and sequence analysis of cDNA.

The mitochondrial isoenzyme of aspartate amino-transferase (mAspAT; subunit Mr 45,000) is synthesized on free polysomes in the cytosol as a precursor of higher Mr (pre-mAspAT; Sonderegger, P., Jaussi, R., Christen, P., and Gehring, H. (1982) J. Biol. Chem. 257, 3339-3345). We have isolated three overlapping cDNA clones that correspond almost to the full length of pre-mAspAT mRNA with 100 nucleotides at the 5' end missing. The mRNA is 2.1 kilobase pairs long and has a 3' noncoding region of 0.7 kilobase pairs. The cDNAs code for the 401 amino acid residues of mAspAT plus an NH2-terminal pre-piece. Deviations from the reported amino acid sequence were found at positions 154 and 202 where the cDNA specifies Gln instead of Glu. The pre-piece consists of 22 amino acid residues, among them 4 arginine and no acidic residues.

A comparative study on enzymatic data from myocardial biopsies and cardiac function in patients who underwent cardiac surgery.

Twenty-three patients underwent cardiac surgery for valve replacement, valve reconstruction, aorto-coronary bypass grafting, aneurysmectomy or combinations of these. Excised cardiac tissue was obtained from left ventricular (LV) papillary muscle (17 patients), LV outflow tract (3 patients), or LV aneurysms (3 patients). A total of 34 myocardial samples, collected from excised cardiac tissue, were analysed for creatine kinase (CK), CK-isoenzymes, cytoplasmic and mitochondrial isoenzymes of aspartate aminotransferase (cAST and mAST, respectively), and lactate dehydrogenase (LDH) isoenzymes. Myocardial CK activity correlated positively with preoperative LV ejection fraction (p less than 0.001), negatively with the preoperatively measured extent of LV wall motion abnormalities (p less than 0.001), and negatively with preoperative LVEDP (p less than 0.02). Myocardial CK activity was negatively correlated with preoperative validity class (p less than 0.005). However, no correlation existed between myocardial CK activity and postoperative validity. Excluding the biopsies from LV aneurysms, myocardial CK activity was positively correlated with the fraction H-subunits in LDH (p = 0.02), and was negatively correlated with the fraction mAST in total AST (p less than 0.005). While cAST activity was proportional to CK activity in the biopsies from VL papillary muscle and LV outflow tract, mAST activity declined only with 2.4 +/- 1.2% per 10% fall of CK. The increase of mAST/cAST ratio with decreasing CK, together with the decrease of LDH-H/LDH and CK-M/CK ratios with decreasing CK, indicated the presence of an adaptation process in a myocardium with low CK activity rather than a process of necrosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum activity of mitochondrial aspartate aminotransferase: a sensitive marker of alcoholism with or without alcoholic hepatitis.

Serum activity of the mitochondrial isoenzyme of aspartate aminotransferase (mAST) was measured with an immunological method in 74 subjects. Fourty-six were chronic alcoholics with (30) or without (16) obvious alcoholic liver disease; 28 were nonalcoholic controls among whom 14 had acute or chronic viral hepatitis, the remaining 14 being healthy individuals. Mean mAST activity was much higher in all the alcoholic subjects, with or without liver disease, 10.4 and 1.95 units per liter, respectively, than in the healthy controls (0.43, p less than 0.001). The mean mAST to total AST ratio was similar in the healthy controls and in the patients with viral hepatitis (2.98 and 3.19%, NS), whereas it was about 4 times higher in the alcoholics with a sensitivity which reached 93% in the patients with alcoholic liver disease and 100% in those without. Both gamma-glutamyl transpeptidase and glutamate dehydrogenase serum activities were far less sensitive and specific. As almost all chronic alcoholics had similar abnormal values of mAST/total AST ratio, this leads to question whether "normal" liver may really exist in any of such subjects.

Radioimmunoassay of aspartate aminotransferase isoenzymes in human serum.

We describe the development of a sensitive, specific radioimmunoassay for the cytoplasmic and mitochondrial isoenzymes of human aspartate aminotransferase (L-aspartate:2-oxoglutarate aminotransferase; EC 2.6.1.1). Isoenzymes from human heart tissue were purified to homogeneity and used to raise high-titer antisera in rabbits. We partly purified the antisera by selective column chromatography. The Bolton-Hunter reagent was used to radioiodinate the isoenzymes. The assay requires 100 microL of serum, includes a solid-phase second-antibody separation, and can be completed in less than 3 h. There was no cross reactivity between the two isoenzymes. As little as 5 micrograms (50 pmol) of each aspartate aminotransferase can be measured per liter of serum.

Correlation of structure and catalysis by aspartate aminotransferase isoenzymes.

Conference Article| June 01 1984 Correlation of structure and catalysis by aspartate aminotransferase isoenzymes PHILIPP CHRISTEN; PHILIPP CHRISTEN *Biochemisches Institut der Universität Zürich, Zürichbergstrasse 4, CH-8028 Zürich, Switzerland Search for other works by this author on: This Site PubMed Google Scholar HEINZ GEHRING; HEINZ GEHRING *Biochemisches Institut der Universität Zürich, Zürichbergstrasse 4, CH-8028 Zürich, Switzerland Search for other works by this author on: This Site PubMed Google Scholar ERIKA SANDMEIER; ERIKA SANDMEIER *Biochemisches Institut der Universität Zürich, Zürichbergstrasse 4, CH-8028 Zürich, Switzerland Search for other works by this author on: This Site PubMed Google Scholar HEINZ KIRSTEN; HEINZ KIRSTEN *Biochemisches Institut der Universität Zürich, Zürichbergstrasse 4, CH-8028 Zürich, Switzerland Search for other works by this author on: This Site PubMed Google Scholar KURT PFISTER; KURT PFISTER *Biochemisches Institut der Universität Zürich, Zürichbergstrasse 4, CH-8028 Zürich, Switzerland Search for other works by this author on: This Site PubMed Google Scholar JOHAN N. JANSONIUS JOHAN N. JANSONIUS †Biozentrum der Universität Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland Search for other works by this author on: This Site PubMed Google Scholar Biochem Soc Trans (1984) 12 (3): 427–430. https://doi.org/10.1042/bst0120427 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Cite Icon Cite Get Permissions Citation PHILIPP CHRISTEN, HEINZ GEHRING, ERIKA SANDMEIER, HEINZ KIRSTEN, KURT PFISTER, JOHAN N. JANSONIUS; Correlation of structure and catalysis by aspartate aminotransferase isoenzymes. Biochem Soc Trans 1 June 1984; 12 (3): 427–430. doi: https://doi.org/10.1042/bst0120427 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsBiochemical Society Transactions Search Advanced Search This content is only available as a PDF. © 1984 Biochemical Society1984 Article PDF first page preview Close Modal You do not currently have access to this content.

Mitochondrial and cytoplasmic isoenzymes of aspartate aminotransferase in sera of patients after myocardial infarction

Mitochondrial and cytoplasmic isoenzymes of aspartate aminotransferase (AST) were studied in the sera of 42 patients following acute myocardial infarction and compared to creatine kinase (CK), lactate dehydrogenase (LDH) and alanine aminotransferase (ALT). Mitochondrial AST(ASTm) was detected in 93% (39/42) of patients. Maximum recorded ASTm activity was 59.5 ± 8.8 U/l and was found 39.4 ± 3.5 hours after the onset of symptoms (chest pain) of myocardial infarction. In contrast the maximum recorded cytoplasmic AST (ASTc) activity was greater (327 ± 23 U/l) and it occurred earlier (33.5 ± 2.2 hours) after onset of infarction compared to ASTm. ASTm correlated significantly ( p < 0.05) with ASTc, LDH and ALT but not with total CK or CK-MB. ASTc correlated significantly ( p < 0.05) with total CK, CK-MB and LDH but not ALT. Maximum recorded ASTm activity was significantly associated with the clinical assessment of left ventricular failure (Killip classification) but not with ventricular arrhythmias. In a subset of 15 patients evaluated with invasive hemodynamic measurements of cardiac output and pulmonary capillary wedge pressure. ASTm correlated significantly ( p < 0.05) and better than CK-MB with the hemodynamic assessment of left ventricular dysfunction. Thus ASTm can be readily identified in sera of patients after acute myocardial infarction and may be of value in the evaluation of patients with acute myocardial infarction.

1H NMR studies of aspartate aminotransferase. Histidyl residues of cytosolic and mitochondrial isoenzymes.

200 MHz proton nuclear magnetic resonance spectra were compared between the cytosolic (cAAT) and mitochondrial (mAAT) isoenzymes of aspartate aminotransferase (EC 2.6.1.1) from pig heart. The pattern of signal distribution in the whole spectral region differed considerably between the two isoenzymes, reflecting the difference in their amino acid sequences. A group of distinct signals were resolved at elevated temperatures (50 to 70 degrees C) in the low field region (9.0 to 7.5 ppm) of the spectra of both isoenzymes in the pyridoxal form. Most of these signals were also observable at 28 degrees C although some showed considerable line broadening. Among resonance lines in this spectral region, cAAT in the pyridoxal form showed four pH-titratable resonances with pKa of 9.54, 6.72, 5.69, and 4.87 at 28 degrees C. Variation in pK and line width of these signals indicated differences in the microenvironment of histidyl residues. On the other hand, mAAT showed six pH-titratable resonances with pKa of 6.73 (peak 2), 6.77 (peak 3), 6.07 (peak 4), 4.71 (peak 5), 4.54 (peak 6), and 4.33 (peak 7). Peaks 2, 3, and 4 were narrow and others were considerably broad. Thus, only part of the histidyl residues present in each isoenzyme (8 and 10 His/monomeric unit of cAAT and mAAT, respectively) appeared on the spectra as pH-titratable resonances. With both isoenzymes, chemical shift and pKa values of these signals obtained for the pyridoxal form were indistinguishable from those for the pyridoxamine form and the borohydride-reduced form. None of the observable signals were affected upon the interaction of cAAT with glutarate. By contrast, peaks 2 and 4 in mAAT showed subtle but distinct chemical shift changes upon complex formation with succinate, suggesting that these two resonances are due to histidyl residues located at the part of the enzyme molecule which undergoes a conformational change upon the interaction with the dicarboxylate.

Organ specificity of glucocorticoid-sensitive tyrosine aminotransferase. Separation from aspartate aminotransferase isoenzymes.

In order to study whether hormone-sensitive tyrosine aminotransferase exists in tissues other than liver, we have devised means to separate the liver-specific enzyme from other enzymes that transaminate tyrosine and to distinguish between the authentic enzyme and the principal "pseudotyrosine aminotransferases," which are the isoenzymes of aspartate aminotransferase. We accomplish this by suppressing proteolysis of the authentic enzyme using a buffer of pH 8.0 containing 0.1 M potassium chloride; enzyme extracted from liver in this buffer migrates as a single peak during chromatography on hydroxylapatite and represents the undegraded native form. A much smaller peak of tyrosine aminotransferase activity elutes at higher ionic strength and corresponds to a mixture of mitochondrial aspartate aminotransferase and partially degraded tyrosine aminotransferase. Cytosolic aspartate aminotransferase, in contrast, adsorbs weakly to the hydroxylapatite column and transaminates tyrosine very poorly although it readily utilizes monoiodotyrosine. The aspartate aminotransferase isoenzymes separate completely from tyrosine aminotransferase during chromatography on DEAE-Sepharose CL-6B. By combining these techniques with the use of specific antibodies, we show that brain, heart, and kidney do not contain tyrosine aminotransferase. Furthermore, we locate both isoenzymes of aspartate aminotransferase on polyacrylamide gels and show that both react histochemically as tyrosine aminotransferases when monoiodotyrosine is used as substrate. Use of these techniques, therefore, permits unambiguous identification of tyrosine aminotransferase and its separation from the background of nonspecific transamination.

Structural and genetic relationships between cytosolic and mitochondrial isoenzymes

The most common type of genetic relationship between cytosolic and mitochondrial isoenzymes will probably be found to be divergent evolution from a common ancestral form. This is firmly established for the aspartate aminotransferases and less directly so in other cases. The two isoenzymes of aspartate aminotransferase have evolved at roughly equal rates at the level of total amino acid sequence but certain limited surface regions of the mitochondrial form have been much more highly conserved than corresponding regions in the cytosolic protein; these regions probably play a role in topogenesis of the mitochondrial isoenzyme. It is of interest that nearly all mitochondrial proteins are initially synthesised as precursors of molecular weight greater than the mature forms. In the case of aspartate aminotransferase, and possibly of other such isoenzymes, the N-terminus of the mature protein is nearly coincident with that of the cytosolic isoenzyme. Hence during evolution either the gene for the mitochondrial isoenzyme has gained an extra coding region for this N-terminal extension or, less likely, the structural gene for the cytosolic form has suffered a sizeable terminal deletion. Cytosolic and mitochondrial superoxide dismutases have not shared a common ancestral form as shown by the fact that their primary structures are completely unrelated. On the other hand, the mitochondrial and prokaryotic enzymes are clearly related. There is now, however, evidence to suggest that some prokaryotes possess a copper/zinc enzyme related to the eukaryotic cytosolic form. Hence the possibility arises that primitive prokaryotes possessed both proteins. The copper/zinc superoxide dismutase has been retained in the cytosol of eukaryotic cells and a few bacterial species.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical and diagnostic significance of aspartate aminotransferase isoenzymes in sera of patients with liver diseases.

Serum aspartate aminotransferase isoenzymes were measured in 123 hospital patients with various liver diseases, using a new and simple immunochemical method. Our findings show the usefulness of this determination in estimating the severity of hepatic damage, especially if accompanied by the measurement of other mitochondrial enzymes. During hepatic damage, the cytoplasmic isoenzyme is found in greater quantities than the mitochondrial isoenzyme, but the level of the latter increases to a greater extent in acute liver diseases. Moreover, the values of mitochondrial aspartate aminotransferase activity and the ratio of mitochondrial to total aspartate aminotransferase in alcoholic hepatitis are higher than expected if so-called hepatic enzymes commonly measured in serum are considered. These results indicate that there is significant mitochondrial damage in alcoholic hepatitis.

10] Pyridoxal phosphate-binding site in enzymes: Reduction and comparison of sequences

Publisher Summary This chapter illustrates pyridoxal phosphate-binding site in enzymes. In pyridoxal phosphate-dependent enzymes, the formyl group at position 4 of pyridoxal-P forms an aldimine bond with the ɛ -amino group of a specific lysyl residue. Involvement of a single particular lysyl residue indicates that there is a specific domain structure favorable for stabilizing the aldimine bond which, otherwise, is readily hydrolyzed. X-Ray analyses of both cytosolic and mitochondrial isoenzymes of aspartate aminotransferase, representative pyridoxal-P-dependent enzymes, provide details of interaction between pyridoxal-P and the enzyme side chains in the coenzyme-accommodating active site. Only the Re side of the aldimine bond is open to solvent, the Si face being shielded from solvent. This stereospecific status of the bound coenzyme has been remarkably identical among a variety of pyridoxal-P-dependent enzymes. At neutral pH, pyridoxal-P absorbs at 390 nm, which shifts more or less to a longer wavelength (410-430 nm) upon the formation of an aldimine linkage with amino compounds or apoenzymes. Pyridoxal-P-aldimine bond is reduced by borohydride or borocyanohydride under mild conditions. The reduction renders the aldimine bond highly stable to hydrolysis. The resulting reduced enzyme is fragmented by either proteolytic or chemical cleavage, followed by isolation of a phosphopyridoxyl peptide and its structural determination.

The proportion of mitochondrial isoenzyme of aspartate aminotransferase is not elevated in Reye's syndrome.

We reexamined a previously reported, highly specific increase in the relative proportion of the mitochondrial isoenzyme of aspartate aminotransferase (AST) in the serum of patients with Reye's Syndrome. Using ion exchange chromatography, we measured mitochondrial, cytosolic, and total AST in serum samples from (1) 10 patients early in the course of Reye's Syndrome; (2) nine controls with normal serum AST; and (3) seven controls with other diseases causing an increase in serum AST. The mitochondrial percentage (2.8 +/- 2.0%) in Reye's Syndrome was significantly lower (P less than 0.05) than that of both the normal control group (6.1 +/- 7.1%) and the group with increased AST (5.6 +/- 4.0%). We thus failed to confirm the previous report of a specific increase in the % of mitochondrial isoenzyme in Reye's Syndrome, and conclude that the % of mitochondrial isoenzyme is not likely to be a useful marker of (or predictor for progression to) Reye's Syndrome.