Photoregulation of an enzymic process by means of a light-sensitive ligand.

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.

Comparative plaque acidogenesis of caries-resistant vs. caries-susceptible adults.

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).

Polyamines of dental plaque in caries-resistant vs. caries-susceptible adults.

Utilizing a sensitive liquid chromatographic system, polyamines were quantitated in three-day plaque from 13 caries-resistant (CR) and 35 caries-susceptible (CS) adults after they had fasted for 12 hours. The values for putrescine and cadaverine were significantly higher in the CR group. This may be attributed to a greater availability of salivary substrate precursors of polyamines and/or higher levels of biosynthetic decarboxylase activities in the CR subjects, or both.

The effect of sucrose and hexitol--containing chewing gums on plaque acidogenesis in vivo.

Comparative quantitation of plaque organic acids formed in vivo in the course of chewing sucrose and sorbitol-mannitol containing gums disclosed that the hexitol gum did not generate any additional lactic, formic, butyric, propionic, acetic or pyruvic acid beyond baseline (0 time) values. In contrast, sucrose-containing gum produced significant increases in lactic and butyric acids. Quantitatively, acetic acid was the major acid in all plaque samples; the values were comparable for both gums at all times, suggesting it was mainly generated from endogenous sources.

Photoregulation of biological activity by photocromic reagents. II. Inhibitors of acetylcholinesterase.

The enzymic activity of acetylcholinesterase can be photoregulated through the mediation of photochromic inhibitors of the enzyme. N-p-phenylazophenyl-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.

Phenothiazine-N-carbonyl chloride, a specific inactivator of chymotrypsin.

Phenothiazine-N-carbonyl chloride inactivated chymotrypsin and trypsin by means of a 1:1 stoicheiometric reaction. Its reaction with chymotrypsin was 29 times as fast as that with trypsin and was inhibited by indole. The reaction of phenothiazine-N-carbonyl chloride with chymotrypsin resembled an enzyme-substrate reaction in which the deacylation step is rate-limiting. Slow deacylation occurred, resulting in complete regeneration of active enzyme in 15h. The pH-rate profile of the inactivation process had a maximum at pH7.8. These data and other evidence indicate that the reaction of phenothiazine-N-carbonyl chloride with chymotrypsin exhibits ;kinetic specificity'. Therefore any hypothesis that attempts to describe the topography of the active site of chymotrypsin should take into account the reactivity of phenothiazine-N-carbonyl chloride. The above findings, as well as recent reports of others, are examined within the context of a hypothesis given in an earlier paper (Erlanger, 1967).

Photoregulation of biological activity by photochromic reagents, IV. A model for diurnal variation of enzymic activity.

Levels of acetylcholinesterase 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 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.