Choline esterase activity rhythm in the ventral nerve cord of scorpion

On the possible mode of action of neurohormones on cholinesterase activity in the ventral nerve cord of scorpion, Heterometrus fulvipes

It is shown that Km of ChE is not affected by the neurohormones but Vmax is increased and decreased in presence of acceleratory and inhibitory neurohormones respectively. Hence it is suggested that the neurohormones might modulate the enzyme activity be altering the maximal velocities (Vmax) rather than affecting the enzyme affinity (Km) towards the substrate.

Human subject experiments to estimate reentry periods for monocrotophos-treated tobacco

Thirteen to fifteen human volunteers worked for eight-hr periods in tobacco fields treated 96, 72, and 48 hr previously with monocrotophos (3-hydroxy-N-methyl-cis-crotonamide dimethyl phosphate). At the 48-hr reentry period, during which time no rainfall occurred, both post-exposure plasma and red blood cell cholinesterase levels of the worker group were depressed from pre-exposure levels although the decline was less than 9% in both cases. Rainfall in excess of one inch fell during the 96- and 72-hr reentry intervals, and no important change in cholinesterase levels was noted. Experiments with mice were in general agreement with the human tests. Dimethyl phosphoric acid in urine of the worker group collected prior to, and three hr after, exposure was unchanged in all cases. Rain appeared to have markedly reduced dislodgable residues.

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.

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.