Parachloromercuribenzoate Research Articles

Chemical modification of membranes. II. Permeation paths for sulfhydryl agents.

The amino-reactive reagent, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS),(1) considerably reduces the uptake of the sulfhydryl agent, parachloromercuriphenylsulfonic acid (PCMBS), but does not reduce its effects on cation permeability and on cation transport. These data indicate that PCMBS enters the membrane by at least two channels, one sensitive and the other insensitive to SITS, with only the latter leading to the cation-controlling sulfhydryl groups. Substitution of phosphate or sulfate for chloride results in an inhibition of PCMBS uptake via the SITS-insensitive pathway. These and other data lead to the conclusion that the SITS-sensitive pathway is the predominant one for anion permeation, and the insensitive one for cation permeation. Parachloromercuribenzoate (PCMB), an agent that is more lipid-soluble than PCMBS, penetrates faster but has a smaller effect on cation permeability. Its uptake is less sensitive to SITS. These and other observations suggest that the cation permeation path involves an aqueous channel in the membrane.

Muscle Contraction produced by Sulphydryl Inhibitors

IT was recently reported1 that the sulphydryl (—SH) agent, parachloromercuribenzoate (PCMB), causes superprecipitation of actomyosin gel. Masking of an —SH group appears to prevent interaction between ATP and some inhibitory site on the protein, thus enabling ATP to induce superprecipitation through reaction with another site. If this phenomenon is related to changes occurring in the actomyosin system during muscle activity, then —SH agents should be expected to produce contraction. Accordingly, several such agents were tested on skeletal muscle, and they were found to cause various types of contractile phenomena.

LOCALIZATION OF ERYTHROCYTE MEMBRANE SULFHYDRYL GROUPS ESSENTIAL FOR GLUCOSE TRANSPORT.

The reactions of three organic mercurial compounds, chlormerodrin, parachloromercuribenzoate (PCMB), and parachloromercuribenzenesulfonate (PCMBS) with intact red blood cells, hemolyzed red cells, hemoglobin solutions, and hemoglobin-free ghosts have been characterized. Both PCMB and PCMBS react with only 2 to 3 sulfhydryl groups per mole of hemoglobin in solution, whereas chlormerodrin reacts with 6 to 7. In hemoglobin-free ghosts, however, all three reagents react with a similar number of sulfhydryl groups, approximately 4 x 10(-17) moles per cell, or about 25 per cent of the total stromal sulfhydryl groups, which react with inorganic mercuric chloride. In the intact cell the membrane imposes a diffusion barrier; chlormerodrin and PCMB penetrate slowly, whereas PCMBS does not. Kinetic studies of chlormerodrin binding to intact cells reveal that the majority of stromal sulfhydryl groups is located inside the diffusion barrier, with only 1 to 1.5 per cent (or 1 to 1,400,000 sites per cell) located outside of this barrier. Reaction of PCMBS with intact cells is limited to this small fraction on the outer membrane surface. All three reagents are capable of inhibiting glucose transport in the red cell. With chlormerodrin and PCMBS it was demonstrated that the inhibition results from interactions with the sulfhydryl groups located on the outer surface of the membrane.