Isoenzymes, multiple enzyme forms, and phylogeny

Nongenetic variation, genetic-environmental interactions and altered gene expression. I. Temperature, photoperiod, diet, pH and sex-related effects

The use of protein electrophoretic data for determining the relationships among species or populations is widespread and generally accepted. However, many confounding factors may alter the results of an electrophoretic study in such a way as to allow erroneous conclusions to be drawn in taxonomic, systematic or population studies. Such variables as temperature, photoperiod, salinity, pH and diet have been shown to influence enzymes and proteins both quantitatively and qualitatively. Production of distinct "cold" and "warm" isozymes or "seasonal" isozymes have been found in a variety of organisms. The factors that are or may be responsible for the appearance of these isozymes is discussed. Most studies that have demonstrated some apparent form of environmentally induced genetic expression have not determined that mechanisms responsible. However, proteolytic modification has been shown to produce seasonal isozymes of fructose 1,6-bisphosphatase in rabbit liver and may account for other seasonal isozymes. Acclimating organisms to various conditions may actually allow detection of cryptic genetic variation and provide valuable data. There are many aspects to consider in designing acclimation experiments, and the conditions used will vary according to the aim of the research. Polyploidy may contribute to the genesis of environmentally regulated isozymes. A review of this literature follows with additional hypotheses and conclusions. Recommendations are given for the resolution of real and potential problems.

Comparative study of esterases in brains of the vertebrates

Disc gel electrophoretic patterns of esterases obtained in the buffer (0.1 M Tris-HCl buffer pH 7.4) extracts of the brains of twelve species belonging to various classes of vertebrates ranging from fishes to mammals are compared. Substrate specificity and inhibitor sensitivity is used to classify the enzymes into different classes of esterases. The pattern obtained does not suggest distribution of any specific enzymes to a particular class of vertebrates nor does it suggest any evolutionary change from fish to mammals. Some fast moving bands are observed in fishes and amphibians. Esterases with active thiol groups (Aryl and Esdp esterases) exhibit wide distribution among the species studied. The enzymes which are resistant to inhibition by eserine, pCMB and DFP (Acetyl and ER esterases) are present in the tetrapods studied.

The concept of isoreceptors: application to the nicotinic acetylcholine receptor and the gamma-aminobutyric acidA/benzodiazepine receptor complex

The concept of isoreceptors offers a possible clue to account for pharmacological and biochemical heterogeneity in specific receptor systems. The existence of isozymes has set the foundation for the definition of isoreceptors. The resulting criteria are applied to two central receptor complexes. Accordingly, the nicotinic acetylcholine receptor is defined as an isoreceptor, and research results on the GABA/benzodiazepine receptor are interpreted under the consideration of the possible existence of isoreceptors.

Phylogenetic receptor research: implications in studying psychiatric and neurological disease

Phylogenetic studies will help to evaluate the structure and function of receptors. We were able to show that the regional heterogeneity of the central benzodiazepine receptor previously described in mammals also applies to avians. In addition, a systematic species comparison of the subunit patterns revealed a certain phylogenetic relationship suggesting evolution by gene duplication and subsequent divergence. In analogy to isozyme systems, these results possibly indicate that the GABA/benzodiazepine receptor is an isoreceptor complex. The implications for neuropsychiatric genetics are discussed.

A survey on the formation and localization of secondary isozymes in mammalia

A survey on the formation of secondary isozymes (= multiple molecular forms of enzymes) is given by means of well-documented enzyme systems. Further examples of a certain type of formation are summarized in tabular form. Eight different classes of enzyme variants deriving from translational processes are discussed. These are: aggregation, polymerization, oxidation and reduction of free SH groups, limited proteolysis, cleavage of carbohydrate residues, deamidation, noncovalent binding of coenzymes, and conformational isomerism. In addition, the intracellular distribution of secondary isozymes is discussed, as are the formation of artificial enzyme variants and the recognition of multiple enzyme forms caused by an exchange of neutral amino acids. About 200 original papers are cited. The reference list was completed in early 1979.

Isolation and characterization of multiple forms of renin from bull kidney

Different forms of renin have been purified from bull kidney by combined gel filtration, affinity chromatography and ion-exchange chromatography. The specific activity of the enzyme was determined by a biochemical method of synthetic substrate and by radioimmunoassay on both synthetic and natural substrates; molecular characterization was carried out by molecular weight determinations, polyacrylamide gel electrophoresis, isoelectric focusing, amino acid analysis and optical rotatory dispersion. Three forms (renin C, D, E) are distinct on the basis of amino acid composition and chromatographic behavior, while possessing the same molecular weight, and displaying only minor differences in specific activity, alpha-helix content and isoelectric point; the occurrence of a group of renin isoenzymes may be suggested. Another form (A) has a lower specific activity and a higher molecular weight (57 000) compared with C, D and E and further differs markedly in chromatographic behavior, amino acid composition, alpha-helix content and isoelectric point, as well as in substrate specificity; it may be regarded as a pseudorenin. The fifth form (B) possesses the highest specific activity and does not correspond to a single molecular form; the presence of two components of different molecular weight (27 000 and 46 000 respectively) has been established both by polyacrylamide gel electrophoresis and isoelectric focusing.