Recognizing species,present and past

Nobody disputes that nature is meaningfully “packaged” in some way. But debate persists over exactly how (and even whether) the boundaries dividing taxa should (can) be drawn. At one end of the scale, some zealots abstrusely deny real existence to higher taxa.¹ At the other, laborers at the taxonomic rock‐face confront genuine challenges in recognizing and delineating the species that systematists agree constitute the most fundamental unit of taxonomic analysis. 2 , 3     

Proteolytic enzymes, past and present

William Beaumont's pioneering research on gastric secretion has been germinal in the discovery of proteolytic enzymes and the elucidation of their chemical structure, physiological roles, and biochemical evolution. Although the mammalian digestive enzymes, notably those of gastric and pancreatic origin, have been among the best characterized, of even greater interest and complexity are those that fulfill regulatory functions by limiting their action on specific peptide bonds in target protein substrates. The difference between digestive and regulatory proteases can best be understood by considering their evolutionary relationships on the basis of the organization of both their genes and the proteins themselves. An analysis of representative members of protease families, notably the mammalian serine proteases, suggests that they are the products of processes of recombination of gene segments that give rise to functionally and structurally distinct domains. The evolutionary variability introduced by combinations of domains appears to be far more restricted than if each protein molecule were the product of a single and unique evolutionary event.     

Schistosomiasis in Indonesia: past and present

Schistosomiasis is endemic in Indonesia in two isolated areas, Lindu valley and Napu valley, both located in the Province of Central Sulawesi. In 1940, a prevalence survey was initiated in Lake Lindu, which indicated a Schistosoma japonicum infection prevalence of 56% among the population of Anca, Tomado and Langko villages. Another survey was conducted in 1973 in Napu valley and very high infection prevalences of up to 72% were found among the population in Winowanga village. Since then, comprehensive studies on the epidemiology and the effects of control have been carried out in 24 endemic villages in both areas. Over the past six decades, schistosomiasis control has been implemented and the average prevalence is now much lower than before the control programme was launched. In 2006, it was 0.49% in 7 villages in Lindu valley. In Napu valley, the average infection prevalence among the population of 17 villages was 1.08% in the same year. Again in 2006, the prevalence of infection in snails ranged from 0 to 13.4% and from 0 to 9.1% in Napu and Lindu valleys, respectively. The highest prevalence among snails was found in Dodolo village. The prevalence of S. japonicum in the reservoir host Rattus spp. ranged from 0 to 20% and the highest prevalence was again found in Dodolo village. Contemporary data suggest that transmission of schistosomiasis is still ongoing in Indonesia despite regular surveillance and control activities covering the whole endemic area.     

Chitosomes: past, present and future

José Ruiz-Herrera's discovery that chitin microfibrils could be made by a fungal extract paved the way for elucidating the intracellular location of chitin synthetase. In collaboration with Charles Bracker, chitosomes were identified as the major reservoir of chitin synthetase in fungi. Unique in size, buoyant density, and membrane thickness, chitosomes were found in a wide range of fungi. Their reversible dissociation into 16S subunits is another unique property of chitosomes. These 16S subunits are the smallest molecular entities known to retain chitin synthetase activity. Further dissociation leads to complete loss of activity. From studies with secretory mutants, yeast researchers concluded that chitosomes were components of the endocytosis pathway. However, key structural and enzymatic characteristics argue in favor of the chitosome being poised for exocytotic delivery rather than endocytotic recycling. The chitosome represents the main vehicle for delivering chitin synthetase to the cell surface. An immediate challenge is to elucidate chitosome ontogeny and the role of proteins encoded by the reported chitin synthetase genes in the structure or function of chitosomes. The ultimate challenge would be to understand how the chitosome integrates with the cell surface to construct the organized microfibrillar skeleton of the fungal cell wall.     

Life: past, present and future

Molecular methods of taxonomy and phylogeny have changed the way in which life on earth is viewed; they have allowed us to transition from a eukaryote-centric (five-kingdoms) view of the planet to one that is peculiarly prokarote-centric, containing three kingdoms, two of which are prokaryotic unicells. These prokaryotes are distinguished from their eukaryotic counterparts by their toughness, tenacity and metabolic diversity. Realization of these features has, in many ways, changed the way we feel about life on earth, about the nature of life past and about the possibility of finding life elsewhere. In essence, the limits of life on this planet have expanded to such a degree that our thoughts of both past and future life have been altered. The abilities of prokaryotes to withstand many extreme conditions has led to the term extremophiles, used to describe the organisms that thrive under conditions thought just a few years ago, to be inconsistent with life. Perhaps the most extensive adaptation to extreme conditions, however, is represented by the ability of many bacteria to survive nutrient conditions not compatible with eukaryotic life. Prokaryotes have evolved to use nearly every redox couple that is in abundance on earth, filling the metabolic niches left behind by the oxygen-using, carbon-eating eukaryotes. This metabolic plasticity leads to a common feature in physically stratified environments of layered microbial communities, chemical indicators of the metabolic diversity of the prokaryotes. Such 'metabolic extremophily' forms a backdrop by which we can view the energy flow of life on this planet, think about what the evolutionary past of the planet might have been, and plan ways to look for life elsewhere, using the knowledge of energy flow on earth.     

Growth hormone-releasing hormone: past and present

The discovery of hypothalamic hypophysiotropic factors confirmed the hypothesis of Green and Harris in the late 1940s. These hormones were isolated from their eutopic site of production (the hypothalamus) with the exception of growth hormone (GH)-releasing hormone (GHRH), which was isolated from an ectopic, tumoral site of production and found to be responsible for acromegaly. Following the isolation, characterization and synthesis of human GHRH, clinical studies were performed and are described below. Circulating levels of GHRH can be measured and provide the basis for the diagnosis of acromegaly related to the ectopic, tumoral production of GHRH. At present, GHRH is used as a test of GH secretion mainly as an adjunct to other agents which modify somatostatin status, or to GH-releasing peptides. Its therapeutic potential in children and the elderly is still under investigation. The role of GHRH in the pulsatile secretion of GH is described.