Biocrystallization

Abstract: Clinical manifestations of malaria primarily result from proliferation of the parasite within the hosts' erythrocytes. During this process, hemoglobin is utilized as the predominant source of nutrition. The malaria parasite digests hemoglobin within the digestive vacuole through a sequential metabolic process involving multiple proteases. Massive degradation of hemoglobin generates large amount of toxic heme. Malaria parasite, however, has evolved a distinct mechanism for detoxification of heme through its conversion into an insoluble crystalline pigment, known as hemozoin. Hemozoin is identical to beta-hematin, which is constituted of cyclic heme dimers arranged in an ordered crystalline structure through intermolecular hydrogen bonding. The exact mechanism of biogenesis of hemozoin in malaria is still obscure and is the subject of intense debate. Hemozoin synthesis is an indispensable process for the parasite and is the target for action of several known antimalarials. The pathway has therefore attracted significant interest for new antimalarial drug discovery research. Formation of beta-hematin may be achieved in vitro under specific chemical and physiochemical conditions through a biocrystallization process. Based on these methods several experimental approaches have been described for the assay of formation of beta-hematin in vitro and screening of compounds as inhibitors of hemozoin synthesis. These assays are primarily based on differential solubility and spectral characteristics of monomeric heme and beta-hematin. Different factors viz., the malaria parasite lysate, lipids extracts, preformed beta-hematin, malarial histidine rich protein II and some unsaturated lipids have been employed for promoting beta-hematin formation in these assays. The assays based on spectrophotometric quantification of beta-hematin or incorporation of (14)C-heme yield reproducible results and have been applied to high throughput screening. Several novel antimalarial pharmacophores have been discovered through these assays.

Abstract: Gold recovery from dilute solutions has always been a subject of great interest due to ever increasing demand of this precious metal. In the present study, an attempt had been made to recover this noble metal in ionic, nanocrystalline, and metallic form using a combination of biosorption, biocrystallization, and pyro-crystallization techniques with Sargassum biomass as biomaterial. Optimization of process parameters revealed that the biosorption capacity increased with a decrease in pH due to an ion-pairing effect. Kinetic studies showed that the biosorption of Au(III) onto Sargassum biomass was a rapid process with more than 90% removal at the initial 15 min. Nonlinear forms of pseudofirst-order and pseudosecond-order models were used to fit the experimental data. The adsorption capacity (Qmax) from the Langmuir model was found to be 32.94 mg/g at pH 2. Maximum desorption of 97.8% was achieved with 2 N NaOH used as desorption medium. Biocrystallization of ionic gold through bioreduction was observed from...

Abstract: Blood-feeding organisms digest hemoglobin, releasing large quantities of heme inside their digestive tracts. Free heme is very toxic, and these organisms have evolved several mechanisms to protect against its deleterious effects. One of these adaptations is the crystallization of heme into the dark-brown pigment hemozoin (Hz). Here we review the process of Hz formation, focusing on organisms other than Plasmodium that have contributed to a better understanding of heme crystallization. Hemozoin has been found in several distinct classes of organisms including protozoa, helminths and insects and Hz formation is the predominant form of heme detoxification. The available evidence indicates that amphiphilic structures such as phospholipid membranes and lipid droplets accompanied by specific proteins play a major role in heme crystallization. Because this process is specific to a number of blood-feeding organisms and absent in their hosts, Hz formation is an attractive target for the development of novel drugs to control illnesses associated with these hematophagous organisms.