Aldolase isoenzymes

Schapira, F., Dreyfus, J. C., and Schapira, G., Fetal-like patterns of lactic dehydrogenase and aldolase isoenzymes in some pathological conditions. Emymol. Biol. Clin. 7, 98-108 (1966). 

Class I aldolases of mammals and other vertebrates can be subdivided into three distinct isoenzymes.143,331 Identification of the parental aldolases A, B, and C has been made from their substrate specificities (ratio of activity towards D-fructose 1,6-bisphosphate and towards D-fructose 1-phosphate), electrophoretic mobilities, tissue distribution, and specific immunological properties. Aldolase A is the major form, present in muscle aldolase B, the predominant form in liver and kidney and aldolase C, present in brain with aldolase A. In tissues where more than one aldolase isoenzyme occurs, a hybrid form is often observed.331... 

Fructose is primarily metabolized in the liver via fructose-1-phosphate. The F-l-P formed can rapidly be converted to glycolytic intermediates, as catalyzed by a liver-specific aldolase isoenzyme, and further to glucose, glycogen, or lactate. 

The four enzymes of the family of dihydroxyacetone phosphate (DHAP)-dependent aldolases fructose-1,6-bisphosphate aldolase (FruA, EC 4.1.2.13), fuculose-1-phosphate aldolase (FucA, EC 4.1.2.17), rhamnulose-1-phosphate aldolase (RhuA, EC 4.1.2.19) and tagatose-1,6-bisphosphate aldolase (TagA, EC 4.1.2.40), catalyze in vivo the reversible asymmetric addition of DHAP to d-glyceraldehyde-3-phosphate (G3P) or L-lactaldehyde, leading to four complementary diastereomers. DHAP-dependent aldolases create two new stereogenic centers, with excellent enantio and diastereoselectivity in many cases. These enzymes are quite specific for the donor substrate DHAP, but accept a wide range of aldehydes as acceptor substrates. There are only two fructose-6-phosphate aldolase isoenzymes reported to be able to use dihydroxyacetone (DHA) as donor substrate (Schiirmann and Sprenger 2001). 

Fic. 4. Aldolase isoenzyme patterns of embryonic chick tissues (M, muscle H, heart and L, liver). All heart and hver extracts of each age were electrophoresed on the same strips. FDP, fructose 1,6-diphosphate as substrate F-l-P, fructose 1-phosphate as substrate. Celhilose-polyacetate electrophoresis according to Penhoet et til. (1966). Reproduced from Lebherz (1972a), with permission. 

Aldolase is also changed in myopathies. The gastrocnemius muscle of chickens with hereditary dystrophy shows the A3C and A2C2 isoenzymes in addition to aldolase A4 (Schapira, 1970). To explain changes in aldolase isoenzyme patterns one can put forward arguments similar to those proposed above for CPK. 

Other examples could be mentioned, and there is some disagreement as to the extent of quafitative and quantitative changes in aldolase isoenzyme pattern of diseased tissues. The problem of the mechanisms underlying reappearances of fetal isoenzyme patterns, as well as the problem of the significance of such changes, are yet to be solved. A key issue is whether the reversion to fetal pattern is real or apparent. Does... 

Fructose bisphosphate aldolase (isoenzyme B, M, 156,000) (EC 4.1.2.13). Fructosemia, fructosuria and hypoglucosemia after intake of fructose. Intracellular accumulation of fructose 1-phosphate, Hyperurate-mia. Hepatomegaly. Renal tubular dysfunction. Intraocular bleeding. Patients symptom-free and healthy if fructose avoided. Aldolase A (muscle and most other tissues) and aldolase C (brain and heart) present and fully active. 

Enzymes, measured in clinical laboratories, for which kits are available include y-glutamyl transferase (GGT), alanine transferase [9000-86-6] (ALT), aldolase, a-amylase [9000-90-2] aspartate aminotransferase [9000-97-9], creatine kinase and its isoenzymes, galactose-l-phosphate uridyl transferase, Hpase, malate dehydrogenase [9001 -64-3], 5 -nucleotidase, phosphohexose isomerase, and pymvate kinase [9001-59-6]. One example is the measurement of aspartate aminotransferase, where the reaction is followed by monitoring the loss of NADH ... 

These enzymes have been found in all plant and animal tissues examined and are absent only from a few specialized bacteria. Three closely related isoenzymes are found in vertebrates.185 186 The much studied rabbit muscle aldolase A is a 158-kDa protein tetramer of identical peptide chains.186 187 Aldolase B, which is lacking in hereditary fructose intolerance, predominates in liver and isoenzyme C in brain.185... 

In brain tissues, specific isoforms of glycolytic enzymes are also expressed there are specific brain isoforms for PFK (PFK-C), fructose-1,6-bisphosphate aldolase (aldolase C), enolase (enolase y), but not for GAPDH. The isoforms bear the same catalytic functions however, they could be specialized to form different ultrastructural entities. For example, muscle PFK (a dissociable tetrameric form) binds to microtubules and bundle them [94, 95], however, the brain isoenzyme (stable tetramer) does not [96]. 

Isoenzymes or isozymes are enzymes from a single species that have the same kind of enzymatic activity but differ in chemical structure. In addition, they may differ in quantitative characteristics such as possessing different Km s with the same substrate and may differ in response to temperature and effectors. Isozymes of more than 100 enzymes have been demonstrated in humans. The most important of these for diagnostic purposes are the isozymes of LDH, CK, alkaline phosphatase, leucine aminopeptidase, acid phosphatase, and aldolase. These have been exploited for differential organ diagnosis. 

The two common isoforms of the insulin receptor (Fig. 11-11) arise because a 36-nucleohde (12-amino acid) exon is spliced out of the mRNA for the shorter protein. Isoenzymes of aldolase and of many other proteins are formed in a similar manner. Frame-shifting during protein synthesis (Chapter 29) and also post-translational alterations may give rise to addihonal modified forms. They are often synthesized in relatively small amounts but may be essenhal to the life of the cell. In addition, genehc variants of almost any protein will be found in any population. These often differ in sequence by a single amino acid. 

Stacey GN, Hoelzl H, Stephenson JR Doyle A (1997) Authentication of animal cell cultures by direct visualisation of DNA, Aldolase gene PCR and isoenzyme analysis. Biologicals 25 75-83. 

The distributions of isoenzymes of aldolase, LD, and CK in the muscles of patients with progressive muscular dystrophy have been found to be similar to those in the earlier stages of development of fetal muscle. The isoenzyme abnormalities in dystrophic muscle have been interpreted as a failure to reach or maintain a normal degree of differentiation. Isoenzyme patterns in regenerating tissues may also show some tendency to approach fetal distributions. This tendency may result from relaxation or modification of control systems in rapidly dividing cells and may account for some of the isoenzyme changes noted (e.g., in muscle in acute polymyositis). 

The isoenzyme patterns of aldolase, pyruvate kinase, and hexosaminidase have also been shown to undergo a change toward fetus-like patterns in hepatoma. 

Aldolase (fructose-1,6-biphosphate aldolase EC 4.1.2,13) catalyzes the reversible conversion of fructose-1,6-biphos-phate to glyceraldehyde 3-phosphate and dihydroxyacetone phosphate. The enzyme is a tetramer of identical subunits of 40 kDa. Three isoenzymes are identified to date aldolases A, B, and C. Aldolase A is the isoenzyme that is expressed in the RBC, but also in muscle and brain. 

The isoenzyme composition of muscle aldolase also shows a change in the direction of the fetal pattern after denervation of the muscle (S4). 

Subsequent cleavage of fructose-1-phosphate, catalyzed by a liver-specific isoenzyme of aldolase, forms... 

Aldolase is named for the mechanism of the forward reaction, which is an aldol cleavage, and the mechanism of the reverse reaction, which is an aldol condensation. The enzyme exists as tissue-specific isoenzymes, which all catalyze the cleavage of fructose 1,6-bisphosphate but differ in their specificities for fructose 1-P. The enzyme uses a lysine residue at the active site to form a covalent bond with the substrate during the course of the reaction. Inability to form this covalent linkage inactivates the enzyme. 

The isoenzyme distribution patterns of LDH and aldolase in rat kidney deserve particular attention. These patterns look as if they have been formed by the superimposition of two isoenzyme distributions, one heavily weighted toward A4-LDH, the other toward B4-LDH. And, in fact, when adult kidney cortex and medulla are analyzed separately they reveal distinct patterns. Cortex contains mostly B4-LDH and medulla mostly A4-LDH (Smith and Kissane, 1963). Medulla contains only aldolase A whereas in cortex both aldolase A and B are present (Lebherz and Rutter, 1969). In chicken heart, the CPK distribution is different in atrium and ventricle, ventricle showing only BB-CPK, atrium a complement of BB-MB-, and MM-CPK (Bogenmann, 1973). It is obvious, therefore, that isoenzymes may be useful in identifying differences in... 

Apparent reversals of isoenzyme transitions associated with normal development have been observed to be associated with several disease states. They may reflect some sort of dedifferentiative process in the cells of the diseased tissue. Or they could represent adaptations within certain cell types to changes in the metabolism of the organism brought about by the presence of a tumor or lesion. A number of workers have demonstrated that in cancerous tissue isoenzyme patterns of LDH (Goldman et al., 1964 Schapira, 1970), aldolase (Matsushima et al., 1968 Schapira, 1970), and hexoldnase (Herzfeld and Greengard, 1972) show shifts toward the fetal patterns of these enzymes. 

Aromatic biosynthesis is regulated by feedback mechanisms. The first step in the biosynthesis of the 3 aromatic amino acids is catalysed by phospho-2-keto-3-deoxy-heptonate aldolase (EC 4.1.2.15). For each aromatic amino acid there is a separate isoenzyme which is subject both to end product inhibition and to repression of its synthesis by the correspond-... 

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