A specific inactivator of chymotrypsin, p-azophenyldiphenylcarbamyl chloride, exists as two geometric isomers, cis and trans, which are interconvertible by means of light. The cis-isomer is five times more reactive than the more stable trans-isomer, and is obtained by exposure of the latter to light of 320 nanometer wavelength. The trans-isomer can be regained by exposure of the cis-isomer to light of 420 nanometer wavelength. This interconversion can be made to occur in aqueous solution in the presence of the enzyme under conditions in which the trans-isomer reacts relatively slowly with chymotrypsin. Thus, it is possible to regulate the rate of inactivation of chymotrypsin by using light of the appropriate wavelength. This system is presented as a model for some of the light-sensitive metabolic systems present in living organisms.
Abstract.-The enzymic activity of acetylcholinesterase can be photoregulated through the mediation of photochromic inhibitors of the enzyme. N-pphenylazophenyl-N-phenylcarbamyl fluoride, an irreversible inhibitor of acetylcholinesterase, exists as two geometric isomers which are interconvertible through the action of light. The cis isomer, which predominates after exposure to light of 320 nm, is more active than the trans isomer, which results from exposure to light of 420 nm. It was possible, therefore, to use light energy to regulate the inactivation of the enzyme. Similarly, levels of acetylcholinesterase activity could be photo-regulated in a completely reversible manner by means of the photochromic reversible inhibitor p-phenylazophenyltrimethylammonium chloride. These experiments can serve as models for similar phenomena observed in nature, particularly in photoperiodic rhythms of higher animals.A system was recently described in which an enzymic process, in itself insensitive to light, could be made subject to photoregulation through the mediation of a light-sensitive effector molecule.1 The photosensitive compound, N-p-phenylazophenyl-N-phenylcarbamyl chloride2 (PAPC), is a specific inactivator of chymotrypsin.3 PAPC is a photochromic (or phototropic) molecule4 which, under the influence of light, can undergo a reversible configurational change involving the N = N bond, to yield either a cis or a trans isomer. The change in structure is influenced by the wavelength of light as follows: 320 nm trans = cis 420 nm Although both isomers could inactivate chymotrypsin, the cis isomer was found to be about five times more active. Conditions were found in which the rate of inactivation by trans PAPC was very slow. Thus, it was possible to "turn off" (i.e., inactivate) the enzyme by exposing a solution of enzyme in the presence of trans PAPC to light of 320 nm. Similarly, experiments in which the inactivation process could be halted by light were also possible by starting with the cis isomer. It was suggested that these experiments could serve as models for certain photosensitive processes found in nature, e.g., phototaxis.5Our investigations have now been extended to the enzyme acetylcholinesterase (AcCh-esterase). Its activity can be regulated in the same way as the activity of chymotrypsin. Moreover, by using a photochromic reversible inhibitor, it was possible to regulate the level of AcCh-esterase activity reversibly, by the action of light.
The authors conducted a comparative study of plaque acids in three-day fasting or resting plaque samples from ten pairs of caries-resistant (CR) and caries-susceptible (CS) subjects chewing a sucrose gum for a period of 45 min. The study disclosed two important differences: 1) The amount and rate of production of lactic acid were lower in the CR group, especially at ten min; and 2) in contrast to lactic acid levels, the level of acetic acid was significantly higher in the CR group at zero time (before chewing), and after 20 and 45 min of chewing the sucrose gum. Both the lower levels of lactic acid and the higher levels of acetic acid are (paradoxically) consistent with the higher plaque pH values reported for CR when compared to CS subjects. High pK' acids (such as acetic, as well as propionic and butyric) can provide a buffering system (acetate-acetic acid) capable of countering the pH decrement generated by the low pK' acids (lactic, formic and pyruvic).
Abstract. Levels of acetyicholinesterase activity can be made to vary in response to the presence or absence of sunlight in a system that can be considered as a model for photoperiodic processes found in nature. The enzyme is rendered photosensitive by the presence of a photochromic inhibitor, N-p-phenylazophenylcarbamyl choline, which changes from a trans to a cis isomer under the influence of the light of the sun and reverts back to the trans isomer in the dark. The two isomers differ in their ability to inhibit acetylcholinesterase, thus rendering the enzyme system responsive to sunlight. The relationship of this system to photoresponsive processes in nature is discussed, and a possible role in photoregulation is suggested for naturally occurring carotenoids.We have recently shown how systems normally insensitive to light (the enzymes chymotrypsin' and acetylcholinesterase2 and the electroplax of the electric eel)3 can be photoregulated by means of photochromic effector molecules. Those molecules share a common p-phenylazophenyl group which, under the influence of light, undergoes a reversible configurational change to yield a cis or trans isomer (Fig. 1). Their ability to induce photoregulation derives from differences in the biochemical activities of the two isomers. For example, carbamylcholine-induced depolarization of the excitable membrane of the electroplax was inhibited unequally by the cis and trans isomers of p-phenylazophenyltrimethylammonium chloride (in Fig. 1, substitute N(CH3)3+Cl-for R1-N-R2).
Three photochromic reagents were synthesized and examined for their ability to inactivate acetylcholinesterase.
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