P-hydroxymercuribenzoic acid

The activity of [i-galactosidasc (P-Gal) was studied on a quartz chip using a static micromixer to mix the enzyme and substrate on the ms time scale. Inhibition by phenylethyl-P-D-thio-galactoside was also studied [1048]. In another report, the enzyme P-Gal was assayed on a chip in which P-Gal would convert a substrate, resoruhn-P-D-galactopyranoside (RBG), to resoruhn to be detected fluorescently [1049]. By varying the substrate concentrations and monitoring the amount of resoruhn by LIF, Michaelis-Menten constants could be determined. In addition, the inhibition constants of phenylethyl-P-D-thiogalactoside, lactose, and p-hydroxymercuribenzoic acid to the enzyme P-Gal were determined [1049]. 

Aqueous solutions of aequorin also emit light upon the addition of various thiol-modification reagents, such as p-quinone, Br2, I2, N-bromosuccinimide, N-ethylmaleimide, iodoacetic acid, and p-hydroxymercuribenzoate (Shimomura et al., 1974b). The luminescence is weak and long-lasting ( 1 hour). The quantum yield varies with the conditions, but seldom exceeds 0.02 at 23-25°C. The luminescence is presumably due to destabilization of the functional moiety caused by the modification of thiol and other groups on the aequorin molecule. 

Although lipophilic and able to diffuse across the cell membrane TH can enter cells more rapidly by facilitated transport systems that tend to be specific for T4 or T3. Based on studies on isolated hepatocytes and RBCs, TH uptake in fish can be blocked by inhibitors of protein binding (phloretin, bromosulphothalein, 5,5 -di phenylhydan-toin and 8-anilino-1-naphthalene sulphonic acid) and by certain sulphydryl blockers (p-hydroxymercuribenzoate and /V-cthylmaleimide)59,63,64. 

Lukert (1972) made the interesting observation, which may not, however, be directly related to substrate specificity, that the attachment of avian, infectious bronchitis virus to monolayers of chicken embryo kidney cells was inhibited not only by the addition of free or bound sialic acid, but by sulfhydryl-containing compounds. Receptors could be destroyed by neuraminidase or p-hydroxymercuribenzoate treatment. The adsorption of Newcastle disease virus, however, was not affected by the addition of sulfhydryl compounds. 

Other compounds tested for their ability to inhibit or activate sialidase include iodoacetamide (10 m). AT-ethylmaleimide (10 m) and Mersalyl (10 m). On partially purified sialidase from pig kidney, these had no effect (Tuppy and Palese, 1968) a-chymotrypsin with sialidase from bovine brain caused an increase in activity (Gielen and Harprecht, 1969) EDTA, p-hydroxymercuribenzoate (formerly was believed to be p-chloromercuribenzoate), tested on sialidase in rat liver and kidney, had no effect (Mahadevan et al., 1967) the bacterial inhibitors 2-deoxy-2,3-dehydroneuraminic acid and p-nitrophenyloxamic acid tested on purified sialidase from rat heart muscle had no effect (Tallman and Brady, 1973) while l-(4-methoxyphenoxymethyl)-3,4-dehydroisoquino-line and p-hydroxymercuribenzoate were inhibitory with ganglioside Goia substrate. The effect of specific inhibitors on purified sialidase may give useful information about the active site, an unknown entity at this time. 

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