Polypeptide kinetic properties

The structures of several dehydrogenases have now been solved. The work on these has been reviewed in depth in the literature, as have their physical and kinetic properties.1,9,10 Some generalizations can be made. As was discussed in Chapter 1, section D6, the subunits may be divided into two domains a catalytic domain, which can be quite variable in structure, and a nucleotide-binding domain, which is formed from a similar overall folding of the polypeptide chain for all the dehydrogenases. The detailed geometry of the nucleotide-binding... 

The enzyme, which has been isolated from many species, is a tetramer of Mr 140 000. The two forms of the enzyme, the H4, predominating in heart muscle, and the M4, predominating in skeletal muscle, give rise to a family of isozymes.46,47 The amino acid composition of the polypeptide chain that constitutes the M4 form is significantly different from that of the H4 form, and the two have different kinetic properties. Despite this, the sites for the association of the subunits had to... 

DNA polymerases perform essential roles in the replication and repair of genetic material. The DNA polymerases of several mesophiles have been extensively characterized, and the structural, biochemical, and kinetic properties of Escherichia coli, yeast, mammalian, and bacteriophage DNA polymerases have been the subject of numerous reviews. " Certain enzymes complement DNA polymerase activity with 3 - -5 -exonuclease (proofreading) activity and/or 5 - 3 -exonuclease activity, which typically reside in separate structural domains on the same polypeptide. To orchestrate DNA replication and repair, both eubacteria and eukaryotes possess multiple DNA polymerases, each with distinct properties, subunit compositions, and physiological roles. In vivo, DNA polymerases require the assistance of numerous accessory proteins to replicate and repair the genome (reviewed ). Based on amino acid sequence homology to E. coli enzymes, DNA polymerases have been classified into at least three distinct families Family A (Pol I-like), Family B (Pol Il-like), and Family C (Pol Ill-like). ... 

These issues can be avoided by performing the synthesis on linear polymers such as poly(ethylene glycol) (PEG) (64,65), as PEG is soluble in a wide range of organic solvents and, when linked to polypeptides, enhances solubilization. Furthermore, Bayer demonstrated that during coupling reactions, PEG-linked amino acids had the same kinetic properties as amino acid esters (66). However, the main problem in liquid-phase peptide synthesis is the separation of linear PEG from the final polypeptide after cleavage. 

Numerous publications have appeared recently on the control of cholesterol biosynthesis. For an account of early work on this topic, the reader is referred to a comprehensive review. Substantial acetoacetyl-CoA thiolase [(l)->(2)] and p-hydroxy-P-methylglutaryl-CoA (HMG-CoA) synthase [E.C.4.1.3.5 (2)->(3)] activities have been reported in the cytoplasmic cell fraction of avian liver. Two cytosolic forms (I and II) of the HMG-CoA synthase, which have been obtained in homogeneous form, have distinctly different electrophoretic and chromatographic properties but similar kinetic properties. Synthase I is composed of a single polypeptide chain of approximately 52000 daltons,... 

Ideally, PFV requires a film of active molecules (monolayer or submonolayer) that behave independently of each other and homogeneously with regard to their electrochemical and catalytic properties. Interactions between centres in neighbouring molecules are naturally minimised by the surrounding polypeptide and ensure that PFV is relatively free from complications induced by intermolecular interactions of the type that frequently distort the voltammetry of surface-confined small molecules. Usually, however, peak widths are larger than expected due to inhomogeneity (dispersion). The activity of enzyme molecules with dispersed and poor interfacial electron-transfer kinetics (low will distort the voltammogram and complicate analysis. 

Furthermore, long-lived meta stable energy minima might exist in relation to the isomeric state of a critical peptide bond [184]. In the metastable state in which the folded forms of a polypeptide chain have similar structural characteristics but differ in their free energy level, the kinetically trapped species could demonstrate properties of a high energy peptide bond isomer [185]. 

In conclusion, the biochemical properties of the APIase function of hsp70 molecular chaperones allow kinetic proofreading of folding by rapid scanning of APIase-sensitive sites of unfolded polypeptide chains. 

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