Sampling Tubes with PHMB Reference: 10949-100 4-(hydroxymercuri)Benzoic Acid(PHMB) is used to inhibit cysteine-protease and acts as a reversible thiol-specific blocker. While blocking the acylated ghrelin degradation, it allows the AcetylCholine Esterase AChE™ used in SPI-Bio EIA kits to work normally, in contrast to serine-protease inhibitors.