Amino acids are the essential molecular components of living organisms on Earth, but the proposed mechanisms for their spontaneous generation have been unable to account for their presence in Earth's early history. The delivery of extraterrestrial organic compounds has been proposed as an alternative to generation on Earth, and some amino acids have been found in several meteorites. Here we report the detection of amino acids in the room-temperature residue of an interstellar ice analogue that was ultraviolet-irradiated in a high vacuum at 12 K. We identified 16 amino acids; the chiral ones showed enantiomeric separation. Some of the identified amino acids are also found in meteorites. Our results demonstrate that the spontaneous generation of amino acids in the interstellar medium is possible, supporting the suggestion that prebiotic molecules could have been delivered to the early Earth by cometary dust, meteorites or interplanetary dust particles.

f-Amyloid protein (A,B) has been implicated in the pathogenesis of Alzheimer disease (AD) by the facts that mutations in its precursor protein lead to the overproduction of A13 (1-5) and that A,B is directly toxic to some types of cells (6)(7)(8). In addition to AD there are numerous other human diseases that are characterized by the deposition of amyloid in various tissues (9). Although these amyloids contain different proteins, all are characterized by the antiparallel }3-sheet conformation of their major protein component (9). As in AD, the tissues surrounding these amyloid deposits frequently show a toxic response. Since the protein components share a secondary structure but have no obvious sequence homology, it is possible that they have a common mechanism for cellular toxicity that is nonspecificially linked to their unique state of peptide conformation or assembly. The alternative is that the responsive cells all have unique receptors for the respective peptides.The mechanism by which AP3 causes cell death is the best understood of the human amyloidoses. Although the molecular details are not completely known, A,3 causes increased H202 accumulation in cells, resulting in free radical-induced lipid peroxidation and, ultimately, cell death (10). The source of H202 is thought to be from the activation of an NADPHlinked oxidase similar to that found in neutrophils, for A,3 toxicity is blocked by relatively specific inhibitors of this enzyme (10). The following experiments address the issue of whether there is a common mechanism of toxicity that is shared by other peptides associated with human amyloidoses and examine how these mechanisms relate to their secondary and tertiary structure. MATERIALS AND METHODSCell Lines. B12 cells are from a collection of cell lines made from nitrosoethylurea-induced rat brain tumors (11). A suspension-growing variant of B12 was selected by growth in Petri dishes over a 6-month period and subsequent cloning. The attached and suspension cell lines have indistinguishable cytotoxic properties versus A,3 (10). Rat primary cultures were made from embryonic day 18 cerebral cortex and cultured on poly(L-lysine)-coated dishes in 50% Dulbecco's modified Eagle medium (DMEM)/50% Ham's F12 medium containing N2 supplements (12). No mitotic inhibitors were required in these minimal conditions, and >95% of the cells were neuronal as defined by staining with neuron-specific enolase and the absence of glial fibrillary acidic protein-positive cells. Dialyzed fetal calf and horse sera were from GIBCO/BRL. The peptides were obtained from Bachem except for the Leu-Lys peptides, which were synthesized according to Brack and Caille (13) and have an average molecular mass ranging from 5000 to 12,000 Da. All peptides-were initially dissolved in water and diluted into culture medium immediately before use. With the exception of poly(Leu), they were soluble in water but formed insoluble aggregates of various sizes in culture medium. The fluorescent dyes were from Molecular Probes, diphenylene iodonium...

Oligomerization of a peptide was attempted in a flow reactor that simulated a submarine hydrothermal system. When fluid containing glycine repeatedly circulated through the hot and cold regions in the reactor, oligopeptides were made from glycine. When divalent ions (such as copper ions) were added under acidic conditions, oligoglycine was elongated up to hexaglycine. This observation suggests that prebiotic monomers could have oligomerized in the vicinity of submarine hydrothermal vents on primitive Earth.

Calcite and aragonite are the two most stable polymorphs of calcium carbonate. Even though they have very similar structures, many organisms are able to selectively deposit one polymorph and not the other. Recent in vitro studies have shown that one or more mollusk shell matrix macromolecules are capable of specific polymorph nucleation, provided they are in an appropriate microenvironment.[1] In this study we examine aspects of the structure and function of some of the components of this b-chitin ± silk fibroin in vitro system. We also show, by scanning electron microscopy, that the chitin framework is very porous, thus facilitating the diffusion of ions and macromolecules into the structure. Fluorescent light microscopy and scanning electron microscopy (SEM) demonstrate that the silk fibroin is intimately associated with the chitin framework. One particular fraction purified from the assemblage of mollusk-shell macromolecules extracted from an aragonitic shell layer is able to specifically induce aragonite crystal formation in vitro. These crystals are needle-shaped, whereas the aragonite crystals induced by the total assemblage of macromolecules are shortened into ellipsoids. This implies that other components in the assemblage modulate crystal growth. Finally, testing of a series of Asp and Leu or Glu and Leu containing synthetic peptides in the in vitro assay system shows that only (Asp-Leu) n is capable of specifically inducing aragonite formation. All these observations demonstrate that polymorph specificity is dependent upon the amino acid sequence, the conformation of specific protein(s) in the mollusk shell and the microenvironment in which crystal nucleation and growth takes place.