Multiple molecular forms

Human interleukin 2, a 133-residue protein, has been separated into multiple molecular forms by selective immunoaffinity chromatography and chromatofocusing. Most of the heterogeneity has been attributed to variations in glycosylation of the threonine residue in position 3 of the polypep-... 

Fig. 4. — Monitoring of the Multiple Molecular Forms of Tomato Pectinesterase by Starch-gel Electrophoresis.98 [ENZ, detection of pectinesterase activity by paper print with pectin and Bromothymol Blue PROT, protein staining with nigrosin O, origin. Key A, 1 crude tomato extract after ammonium sulfate salting-out, and dialysis 2 pectinesterase fraction from column of DEAE-Sephadex A-50 3 and 4 pectinesterase fractions from column of Sephadex G-75. B, Two parts of the same gel after horizontal slicing 1, 500 fig of the isolated form of pectinesterase from a column of CM-Seph-adex C-50 with 175 mM phosphate-sodium chloride buffer 2, active fraction at 150 mM buffer 4 and 5, 250 fig and 1 mg of the isolated form of pectinesterase, respectively.]...

By use of starch-gel electrophoresis175,195 and disc electrophoresis196 and various separation methods, D-galacturonanases were found to occur as multiple molecular forms.167,173-175,184,197... 

The method was used in a modified form for the purification of endo-D-galacturonanase from tomatoes.212 Elution from the column by use of a linear pH gradient led to the separation of pectinesterase and of three multiple molecular forms of endo-D-galacturonanase dif-... 

Cholinesterases are subdivided into acetylcholinesterase and cholinesterase, one with a narrow, the other with broad substrate specificity [109-112], Both enzymes exist in multiple molecular forms distinguishable by their subunits association (Fig. 2.4). The hydrodynamic properties of these associations have allowed globular (G) and asymmetric (A) forms to be distinguished. The G forms can be hydrophilic (water-soluble, and excreted into body fluids) or amphiphilic (membrane-bound). The homomeric class exists... 

D. R. Lynch, S. H. Snyder (1986). Neuropeptides multiple molecular forms, metabolic pathways, and receptors. Annu. Rev. Biochem. 55 773-799. 

The liver enzyme exists in two forms, E and S, which differ only by some six residues in their amino acid sequence.13 Only the S is active toward 3-/3-hydroxysteroids, but both forms are active toward ethanol. None of the known amino acid differences is located in the subunit interfaces. Accordingly, E and S chains combine in statistical ratios to form EE, SS, and ES dimers. These different species are termed isozymes, which means that they are multiple molecular forms of the same enzyme. When it is isolated from liver, the enzyme consists of about 40 to 60% of the EE dimer, the remainder being SS and ES. 

Benzodiazepine receptors. There are multiple molecular forms of benzodiazepine receptors, and there is continuing debate about how differences in the amino acid com-... 

Edsall, J. Multiple molecular forms of carbonic anhydrase in erythrocytes. Ann. N. Y. 

Isozyme existence of two or more compounds possessing the same molecular and structural formulae but having different spatial configurations. Multiple molecular forms of an enzyme within the same individual. 

N. Takahashi, Y. Yasuda, K. Goto, T. Miyake, and T. Muradii, Multiple molecular forms of stem bromelain. Isolation and characterization of two closely related cotn-nmiMitfl- SHI and SB2. J. Riochem. fTatval 74 355 f 19731. 

It is now recognised that a substantial number of proteins, especially enzymes, are polymorphic in that they exist in the cell as multiple molecular forms differing in certain of their physico-chemical properties. Each form of a polymorphic enzyme is called an isoenzyme or isozyme. Electrophoretic techniques provide convenient methods whereby this protein heterogeneity can be investigated and the approach has been widely exploited to characterise parasites. In short, aqueous parasite extracts are electro-phoresed, or focused isoelectrically, and separated proteins are stained generally (usually with Coomassie Blue) or more specifically with a histochemical (enzyme) stain (the zymogram technique). Further details of individual procedures and the use of the approach in parasite identification are to be found in a number of recent reviews (104,258,413,536,615,856). 

Flatmark T (1967) Multiple molecular forms of bovine heart cytochrome c V. A comparative study of their physicochemical properties and their reactions in biological systems. J Biol Chem 24 2454-2459... 

The enzyme can occur in a variety of multiple molecular forms, named isoenzymes or isozymes. Such isoenzymes have the same enzymatic activity but can be separated by electrophoresis. Nagle and Haard (1975) separated the isoperoxidases of bananas into six anionic and one cationic component by gel electrophoresis. By using other methods of separation, an even greater number of isoenzymes was demonstrated. 

The purification of acid phosphatase from the human prostate was undertaken, and high degrees of purity were obtained, before any solid information was available concerning the intracellular distribution of this enzyme or its existence in multiple molecular forms or isoenzymes. Accordingly, in this review several methods of purification will be described first, and the other aspects will then be considered. 

The purification of acid phosphatase from the human liver and the description of its properties do not appear to have been accomplished. Partly, this may be due to the inherent difiBculty of obtaining normal, fresh human material in amounts substantial enough for purification. However, because of the cellular and physiological importance of acid phosphatase, it is advisable to describe in the present section the purifications of the enzyme from rat and bovine liver. Moreover, since these purifications were accomplished with the awareness that acid phosphatase from this source might be present in multiple molecular forms, the descriptions will naturally involve a consideration of the isoenzymes and their properties. 

Figure 1 Subunit structure of the multiple molecular forms of ChEs. G, globular forms A, asymmetric forms with collagen-like tails. Each circle is a catalytic subunit disulfide bridges indicated by S-S as found in the electric organ of the electric eel. (Modified from Brimijoin WS (1992) US EPA Workshop on Cholinesterase Methodologies.)...

Another category of multiple molecular forms can arise when enzymes are ofigomeric and consist of molecules made up of subunits. The association of different types of subunits in various combinations gives rise to a range of active enzyme molecules. When the subunits are derived from different structural genes, either multiple loci or multiple alleles, the hybrid molecules so formed are called hybrid isoenzymes. The ability to form hybrid isoenzymes is evidence of considerable structural similarities between the different subunits. Hybrid isoenzymes can be formed in vitro, but they are also formed in vivo in cells in which the different types of constituent subunits are present in the same sub-ceUular compartment. 

CCK is a linear polypeptide that exists in multiple molecular forms. The first form isolated was the 33-amino acid peptide CCK-33. Other major forms are CCK-8, CCK-39, and CCK-58. In all forms, the five C-terminal amino acids are identical to those of gastrin and are necessary, together with a sulfated tyrosyl residue, for physiological activity. All of the forms of CCK are produced by enzymatic cleavage of a single 115-amino acid precursor, preprocholecystokinin. 

Kamel S, Brazier M, Neri V, Picard C, Samson L, Desmet G, Sebert JL. Multiple molecular forms of pyridinoline cross-lmlcs excreted in human urine evaluated by chromatographic and immunoassay methods. J Bone Miner Res 1995 10 1385-92. 

Gastric inhibitory peptide (GIP) is found in the K cells of the duodenum and jejunum It consists of 43 amino acid residues and occurs in multiple molecular forms. Its secretion is stimulated by the presence of glucose and lipids in the duodenum. It has two main functions ... 

Also, each type of these ion channels with receptor property exists in multiple molecular forms, offering large putative opportunities for selective ligands. They are divided into three main families according to the number... 

This order of evaluation (biochemical, first starch gel, second) is amply justified from our own experiences and the consensus of opinion at a recent symposium on multiple molecular forms of enzymes. In particular, heterogeneity of human intestinal alkaline phosphatase on starch gel was reported by Moss (M34) and Fishman and Kreisher (F9, K25). A certain amount of LPSAP intestinal enzyme may occupy the same position that liver alkaline phosphatase migrates to. On the other hand, more than one band in nonliver positions can be produced by intestine. Another similar situation is seen with placental alkaline phosphatase, which may show three bands. Consequently, the starch-gel data can be correlated with biochemical studies only if the nature and organ source of the preparation are known in advance. 

---