Nonenzymatic Methods For The Preferential And Selective Cleavage And Modification Of Proteins

Selective inhibition of urea transport by oxidizing agents. Evidence for a site of inhibition behond the generation of cyclic AMP

Urea and water transport across the toad bladder epithelial cell appears to take place through independent vasopressin-stimulated pathways. Agents such as chromate, for example, when added to the luminal bathing medium, inhibit urea transport without inhibiting osmotic water flow, providing evidence for such independent pathways. In the present study, selective inhibition of urea transport is shown for permanganate and methylene blue, which like chromate, are oxidizing agents. Permanganate inhibits urea transport irreversibly, while methylene blue acts reversibly. Not all oxidizing agents are inhibitory; perchlorate, peroxide and ferricyanide have no effect on urea transport or water flow. Permanganate and chromate both act at a point beyond the generation of cyclic AMP, since they continue to inhibit urea transport in bladders treated with exogenous cyclic AMP, 8-bromoadenosine 3', 5'-cyclic monophosphate, and a combination of cyclic AMP and theophylline. These findings suggest that selective inhibition of urea transport can be brought about by oxidation of one or more components in its transport pathway, and that, in the case of chromate and permanganate, these components may be in the luminal membrane itself.

Activation of liver alcohol dehydrogenases by imidoesters generated in solution

Various omega-halogenated carboxy acids and amides were evaluated as potential active-site-directed reagents for alcohol dehydrogenase. 2-Bromoacetamide and bromoacetic and 3-bromopropionic acids inactivated the enzyme; AMP, NAD+, and NADH markedly decreased the rate of inactivation. Some omega-halogenated carboxyamides, X(CH2)nCONH2, increased the activity of the enzyme with the rate and extent of activation depending on the number of methylene units (n) in the order 3 greater than 4 greater than 2 and on X in the order Br greater than Cl. 4-Chlorobutyramide (0.1 M) activated the horse liver enzyme 20-fold in 24 hr at pH 8.0 and 25 degrees. The activation was not prevented by AMP or 2,2-bipyridine, but was by NADH. The kinetic constants and turnover numbers for human and horse liver alcohol dehydrogenases treated with chlorobutyramide were increased markedly compared to those for native enzymes. Alcohol dehydrogenase treated with chlorobutyramide was not further activated by methyl picolinimidate, an imidoester which activates native enzyme by modifying amino groups in the active sites. Chlorobutyramide does not appear to react directly with the enzyme but cyclizes in the reaction medium to form an intermediate imidoester, 2-iminotetrahydrofuran, which reacts with most of the amino groups of the enzyme.

Mouse immunoglobulin subclasses: cyanogen bromide fragments and partial sequence of a gamma1 chain

The purification and characterisation of all the cyanogen bromide fragments of MOPC 21 heavy (gamma1) chain is described. The ten BrCN fragments account for the whole chain. Four of these fragments have been used to establish the sequence of the C-terminal stretch (138 residues) that includes the entire CH3 and a part of the CH2 homology regions. A comparison of this sequence with homologous sequences is presented. Mouse gamma1 and gamma2 proteins differ much more than the gamma subclasses in humans and in other species. The comparison further suggests that the four human gamma subclasses and mouse gamma1 have a common ancestor which differs from the mouse gamma2 ancestor. Unlike other subclasses, mouse gamma1 and gamma2 genes have diverged before speciation.

State and reactivity of tryptophyl residues in two bacterial proteases from Sorangium sp

The state and reactivity of tryptophyl residues in two proteolytic enzymes from Sorangium sp. were investigated by means of the following methods: spectrophotometric oxidation of tryptophans with N-bromosuccinimide, 2-hydroxy-5-nitrobenzyl bromide, and H2O2 in dioxane, optical rotatory dispersion, ultraviolet difference spectrophotometry, solvent perturbation and viscosity measurements. Out of two tryptophyl residues/molecule of alpha-lytic protease, one appears to be completely buried, while the other seems to be exposed. None of these two residues seem to be responsible for the activity of the enzyme. The beta-lytic protease undergoes an irreversible conformational transition between pH 5.0 and 3.5. Out of total four tryptophyl residues/molecule, only one is fully exposed at neutral pH. The other three are gradually exposed in the pH transition region. The degree of exposure and the dimensions of "cavities" shielding tryptophyl residues were estimated. The tryptophyl residues of of beta-lytic protease do not seem to participate in substrate binding or the active site; they are rather one of the determinants of the conformational state of the enzyme.

Conformational and functional studies of chemically modified cytochromes: N-bromosuccinimide- and formyl-cytochromes c

N-bromosuccinimide-cytochromes c (Myer, Y. P. (1972), Biochemistry 11, 4195) and formyl-cytochrome c (Aviram, I and Schejter, A. (1971), Biochim. Biophys. Acta 229, 113) have been chromatographically purified, and the resulting components have been characterized in terms of their structure, conformation, and function. The activity measurements are considered in terms of the oxidizability, as the transference of an electron to solubilized cytochrome c oxidase, and reducibility, as the tendency to accept an electron from NADH-cytochrome c reductase. Conformational characterization has been carried out by absorption measurements, pH-spectroscopic behavior, circular dichroism, thermal denaturation, ionization of phenolic hydroxyls, the tendency to form the CO complex, and autoxidation with molecular oxygen. NBS-cytochrome c yields two major components, the relative proportions of which, with increasing modification of the protein, exhibit a pattern typical of the formation of the two in a consecutive manner. The first product contains the modification of the Trp-59 and Met-65 side chains, and the second contains the added modification of Met-80. The former in both valence states of iron is more or less like the native protein, except for an apparently slightly loosened heme crevice; the latter, as in other modifications involving modification of centrally coordinated Met-80, was found to be in a conformational state characteristic of the native protein with a disrupted central coordination complex, a loosened heme crevice, and small, but finite derangement of the polypeptide conformation. Functionally, the first component reflected 55% of the reducibility property and an unimpaired oxidizability property, while the latter exhibited derangement of both aspects of cytochrome c activity. Formyl-cytochrome c yielded a single component with modification of Trp-59. Conformationally, in both valence states, it is a molecular form with a disrupted central coordination complex, a loosened heme crevice, and gross derangement of the overall protein conformation. It exhibits a minimal reducibility property, 12%, whereas it retains a native-like tendency to transfer an electron to cytochrome c oxidase. The data from the NBS-cytochrome c components are analyzed with reference to the two forms in the earlier studies of the unpurified preparations. The results are found to be in agreement with one another. The selectivity between the reducibility and the oxidizability exhibited by the first NBS component and formyl-cytochrome c, irrespective of significant differences in the conformational and coordinational configurations of the two, has been viewed in light of a two-path, two-function model for oxidoreduction, as well as with reference to conformational and structural requirements for the oxidizability and reducibility properties of the molecule.

Amino acid sequences around the cysteine residues of rabbit muscle triose phosphate isomerase

1. The nature of the subunits in rabbit muscle triose phosphate isomerase has been investigated. 2. Amino acid analyses show that there are five cysteine residues and two methionine residues/subunit. 3. The amino acid sequences around the cysteine residues have been determined; these account for about 75 residues. 4. Cleavage at the methionine residues with cyanogen bromide gave three fragments. 5. These results show that the subunits correspond to polypeptide chains, containing about 230 amino acid residues. The chains in triose phosphate isomerase seem to be shorter than those of other glycolytic enzymes.