Role Of Sulphydryl Groups Research Articles

Benzylmercaptan (benzylthiol) and dibenzyldisulphide from the marine sponge Crella spinulata, (Hentschel) (Poecilosclerida: Crellidae)

Benzylmercaptan (benzylthiol) and its oxidised product dibenzyldisulphide have been isolated and characterised from the marine sponge Crella spinulata (Hentschel) found in the Great Barrier Reef, northern Australia. The structures of the two compounds were determined on the basis of their spectral and chemical properties. These two compounds were found only in gravid females collected during the reproductive season. The biochemical interest of these sulphur-containing compounds in the gravid females is briefly discussed in relation to the role of sulphydryl groups in biological systems.

The role of sulphydryl groups in efflux of taurine and GABA from cerebral cortical cells.

1. Effluxes of taurine and GABA from pre-loaded cells in slices of rat cerebral cortex in isosmotic media is enhanced by the -SH reagent p-chloromercuriphenylsulphonic acid (pCMPS) (100 microM) accompanied by moderate swelling. Those effects were more pronounced with GABA than with taurine. N-ethylmaleimide (NEM) (100 microM) had only slight affects on these variables. 2. The acceleration of effluxes that occurs when medium osmolality is reduced from 315 to 265 mosmol/kg is blocked by NEM and by pCMPS, with pronounced cell swelling. 3. The inhibitory effects of these reagents on efflux is abolished when cell swelling is prevented by the addition of 25 mM sucrose to hyposmotic incubation media (with equimolar reduction in NaCl concentration). 4. Pre-exposure of slices to dithiothreitol (DTT) (100 microM) blocks the effects of NEM and pCMPS on GABA efflux in hyposmotic media, but has no effect on taurine efflux. 5. The cell membrane and cytoskeletal responses which may underlie these effects are briefly discussed.

The effect of copper on frog skin. The role of sulphydryl groups

1. 1. Cu 2+ at a concentration of 10 −4 M, when applied to the external side of the frog skin produces an increase in the short-circuit current ( I sc). 2. 2. This effect was studied in skins of Rana temporaria adapted to cold (5°C) and room temperature (20°C), skins of Rana pipiens adapted to cold, and the results compared with those obtained previously with Rana ribibunda. 3. 3. The observed effect is less dependent upon the adaptation to cold than upon the functional state of the skin: skins with low short circuit currents have a bigger response to Cu 2+ than skins with high I sc. 4. 4. A species difference cannot be ruled out since skins of Rana ribibunda exhibiting high I sc give good responses to Cu 2+. 5. 5. 5,5′-dithiobis(2-nitrobenzoic acid), a sulphydryl-oxidizing reagent, produces an effect similar to that of Cu 2+, and dithiothreitol an SH-reducing agent, reverses the effect of this ion. 6. 6. Cu 2+ also induces an increase in the unidirectional K + fluxes and unmasks a net outward potassium flux. 7. 7. The outward K + flux induced by Cu 2+ is sensitive to ouabain. 8. 8. It is concluded that Cu 2+ increases the permeability of the external barrier of the frog skin to Na + and K +, probably by reacting with SH groups.

Role of Sulphydryl Groups in Adenosine Deaminase

The reactivity and the role of sulphydryl groups in adenosine deaminase have been investigated. In the sodium dodecylsulphate-denatured enzyme 2.1 sulphydryl groups are titratable with p-mercuribenzoate. The native enzyme is inactivated by p-mercuribenzoate or phenylmercuric acetate and a stoichiometric relationship exists between the equivalents of mercaptide formed and the inactivation of the enzyme. Substrate analogs protect the enzyme againstp-mercuribenzoate and phenylmercuric acetate inactivation. Iodoacetamide, iodoacetate, and N-ethylmaleimide, which do not affect the enzyme activity, do not react with sulphydryl groups. The results show that a sulphydryl group unreactive towards the alkylating reagents is essential in some way for the enzymatic activity. The lack of reactivity of the essential sulphydryl group with alkylating reagents suggests that the sulphydryl group may be contained in a hydrophobic region of the enzyme molecule.

Role of sulphydryl groups in adenosine deaminase.

The reactivity and the role of sulphydryl groups in adenosine deaminase have been investigated. In the sodium dodecylsulphate-denatured enzyme 2.1 sulphydryl groups are titratable with p-mercuribenzoate. The native enzyme is inactivated by p-mercuribenzoate or phenyl-mercuric acetate and a stoichiometric relationship exists between the equivalents of mercaptide formed and the inactivation of the enzyme. Substrate analogs protect the enzyme against p-mercuribenzoate and phenylmercuric acetate inactivation. Iodoacetamide, iodoacetate, and N-ethylmaleimide, which do not affect the enzyme activity, do not react with sulphydryl groups. The results show that a sulphydryl group unreactive towards the alkylating reagents is essential in some way for the enzymatic activity. The lack of reactivity of the essential sulphydryl group with alkylating reagents suggests that the sulphydryl group may be contained in a hydrophobic region of the enzyme molecule.

The role of sulphydryl groups in soybean beta-amylase.

Summary This research was undertaken to explore the possible role of sulphydryl groups in the activity of soybean β -amylase ( α -1,4 glucan maltohydrolase, EC 3.2.1.2). The dependence of initial velocity and the independence of K m on pH, as well as the non-competitive inhibition pattern of soybean β -amylase by p -mercuribenzoate (PMB), indicate that sulphydryl groups do not participate in binding the substrate and their role in enzymatic action is related to the catalytic step only. The extent of inhibition of soybean β -amylase by PMB is inversely related to the concentration of the acetate buffer used, indicating the “protecting” effect of acetate ions. “Competitive-like” inhibition of β -amylase by PMB was achieved when the concentration of acetate buffer used in the assay was changed in parallel with the dilution of the substrate. Similar results were obtained with crystalline sweet potato β -amylase. Partial titration of soybean β -amylase by PMB inhibited the activity to different extents: titration of one of the five SH groups present in one enzyme molecule affects activity only very slightly, whereas titration of all the 5 SH groups results in almost complete loss of activity.

Role of Sulphydryl Groups in the Long-range Elasticity of Wool

FIBRES of wool and hair may be stretched nearly 100 per cent in water at room temperature, and they return to their original lengths on being released. If a fibre is stretched more than about 30 per cent, or if stretched very slowly to any extension and then released, subsequent stretching requires less energy, indicating that an irreversible change has taken place1. In explanation of these effects it has been postulated that hydrolysis of disulphide bonds occurs during stretching to give sulphydryl and sulphenic-acid groups; but direct evidence for the production of either of these in wool or hair is lacking2,3.

THE CHEMISTRY OF VISION

SUMMARYAn account is given of the isolation of the outer segments of retinal rods, their internal structure as revealed by the electron microscope, and their chemical composition.The relationship between action spectra (e.g. the scotopic luminosity curve) and absorption spectra is discussed. Provided certain conditions are satisfied, the chemist is able to compare the absorption spectra of pigments isolated from the retina with action spectra which have been recorded for the same type of retina by the physiologist. Thus the absorption spectrum of rhodopsin corresponds to the scotopic luminosity curve. If there was general agreement on a theory of colour vision, this would give valuable information concerning the number of photosensitive pigments to be expected.At present the only photosensitive pigments whose existence is unequivocal are rhodopsin (found in mammals, birds, reptiles, Amphibia, most fish and the squid), porphyropsin (found in some fish and Amphibia) and iodopsin (found so far only in the fowl). Recent claims to have extracted other pigments are discussed.The extraction and examination of rhodopsin is described. Until recently the various products obtained from rhodopsin by the action of light were characterized by their absoprtion spectra only. These consisted of retinene, indicator yellow, lumirhodopsin, meta‐rhodopsin and iso‐rhodopsin.The retina has an enzyme, believed to be identical with alcohol dehydrogenase, which catalyses the interconversion of vitamin A and retinene in the presence of coenzyme 1.It has been found possible to effect the regeneration of rhodopsin in vitro. Wald and his co‐workers have shown that a system containing retinene (or vitamin A, coenzyme i and alcohol dehydrogenase) and the specific protein of rhodopsin, ‘opsin’, will synthesize rhodopsin. However, these workers found that synthetic vitamin A or retinene was not effective, but could be made so by exposure to light. Collins and his co‐workers have obtained regeneration in vitro using synthetic vitamin A or retinene; their systems appear to be nearly complete. They have also shown that pyridoxal phosphate augments the amount of regeneration, although no explanation can be given of this result. The rhodopsin system is outlined in a diagram and table.In the next section an account is given of the results of chemical work aimed at identifying the pigments known only by their absorption spectra. The amounts of these pigments are too small to be isolated and indirect methods have to be used. Retinene has now been identified as vitamin A aldehyde. Indicator yellow has been shown not to be an artifact (as suggested by some workers), and to be a Schiffs base of retinene (an N‐substituted retinene imine). However, the structure of the acid form of indicator yellow is still unknown. Because of their possible connection with visual pigments, a brief account is given of vitamin A amine and methylamine. Certain other reactions of retinene are described (e.g. the reaction with sulphydryl groups) in order to assist the discussion of the nature of rhodopsin itself.The significance of the fact that vitamin A, retinene and retinene methylimine react with antimony trichloride, sulphuric acid and phosphoric acid to give compounds which have absorption spectra resembling the action spectra obtained by physiologists in various retinas, is discussed.The outstanding problems are: (1) the structure of acid indicator yellow, (2) the structure of active‐vitamin A and active‐retinene, (3) the role of pyridoxal phosphate, and (4) the role of sulphydryl groups. Possible alternative explanations are presented, and the evidence for and against discussed.I am greatly indebted to Prof. R. A. Morton, F.R.S., for his many helpful criticisms and advice.

Role of Sulphydryl Groups in the Oxidation of Pyruvate

Role of Sulphydryl Groups in the Oxidation of Pyruvate

The role of sulphydryl groups in the interaction of myosin and actin

1. 1. The interaction of actin and myosin in 0.5 M-KCl is not of normal electrostatic type but depends upon the presence of SH groups in the myosin partner. 2. 2. The SH groups concerned are also connected with the adenosinetriphosphatase activity of myosin. Their oxidation by reagents such as iodosobenzoate, hydrogen peroxide, iodine, substitution by chloromercuribenzoate, or alkylation by iodoacetamide lead to a diminution of enzyme activity and of actomyosin-forming ability, the two properties declining at the same rate. 3. 3. The groups concerned are mainly, but not entirely, those which give the nitroprusside test and are accessible to oxidants. 4. 4. Whether a specific chemical grouping is necessary in the actin partner is not known, though several possibilities have been explored. 5. 5. The findings elucidate why adenosinetriphosphate, which is the substrate for the enzyme reaction, so profoundly modifies the colloid reaction. It is suggested that enzymes utilizing adenosinetriphosphate are always of SH character. 6. 6. The results are discussed in relation to the earlier work of Szent-Györgyi and the Szeged school.