Directly active mutagens are formed on exposure of the promutagen benzo[a]pyrene to gaseous pollutants in smog. In simulated atmospheres containing 1 part per million nitrogen dioxide and traces of nitric acid, directly mutagenic nitro derivatives are readily formed from both benzo[a]pyrene and perylene, a non-mutagen in the Ames reversion assay. Possible formation of direct mutagens by such reactions on sample collection filters, in exhaust effluents, and in the atmosphere should be recognized.

Human axillary odor is known to be formed upon the action of Corynebacteria sp. on odorless axilla secretions. The known axilla odor determinant 3-methyl-2-hexenoic acid was identified in hydrolyzed axilla secretions along with a chemically related compound, 3-hydroxy-3-methylhexanoic acid. The natural precursors of both these acids were purified from non-hydrolyzed axilla secretions. From liquid chromatography/ mass spectrometry analysis, it appeared that the acids are covalently linked to a glutamine residue in fresh axilla secretions, and the corresponding conjugates were synthesized for confirmation. Bacterial isolates obtained from the human axilla and belonging to the Corynebacteria were found to release the acids from these odorless precursors in vitro. A Zn 2؉ -dependent aminoacylase mediating this cleavage was purified from Corynebacterium striatum Ax20, and the corresponding gene agaA was cloned and heterologously expressed in Escherichia coli. The enzyme is highly specific for the glutamine residue but has a low specificity for the acyl part of the substrate. agaA is closely related to many genes coding for enzymes involved in the cleavage of N-terminal acyl and aryl substituents from amino acids. This is the first report of the structure elucidation of precursors for human body odorants and the isolation of the bacterial enzyme involved in their cleavage.The axilla region of humans contains a dense arrangement of apocrine, eccrine, and sebaceous glands, and it is an everyday experience, that volatile substances emanating from these areas make a key contribution to human body odor. Although this odor is perceived by today's society as mainly unpleasant, several studies indicate that it may contain chemical signals that affect the menstrual cycle (1) or that may be involved in a major histocompatibility complex allele-dependent mate selection (2). These studies point to an important role of body odors in the evolutionary history of man.Sweat as it is secreted by axillary glands is odorless. Since the pioneering work of Shelley et al. (3), it is known that (a) the typical strong axilla odor can only be released from apocrine secretions, and (b) that the action of skin bacteria is needed to generate the odoriferous compounds from non-smelling molecules present in these secretions. Indeed, the axilla is a skin region supporting a dense bacterial population, which is dominated by the two genera Staphylococcus and Corynebacteria (4, 5). Most individuals carry a flora that is dominated by either one of these two genera, and a strong correlation was found between a high population of Corynebacteria and a strong axillary odor formation (4, 6). As a practical consequence of these findings, halogenated antibacterials and aluminum preparations for reducing the bacterial population have become the main active ingredient of commercial deodorants for the last 40 years. The scientific conclusion from this early work was that axilla secretions contain non-odoriferous precursors that must be transformed by bacterial en...

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ficient quality to be used for matched spatial filter recognition of the object, which is the ultimate goal. There is a considerable reduction in terms of time and cost with this system in comparison to other input methods available for coherent image processing. AcknowledgmentWe thank Aaron Gara and General Motors Corp. for the use of their liquid crystal image panel.

Human axillary odor is known to be formed upon the action of Corynebacteria sp. on per se odorless axilla secretions. Besides the known odoriferous acids, we report the occurrence in human axilla secretions of four odoriferous sulfanylalkanols, namely 3-sulfanylhexan-1-ol (3), 2-methyl-3-sulfanylbutan-1-ol (4), 3-sulfanylpentan-1-ol (5), and 3-methyl-3-sulfanylhexan-1-ol (6). These compounds have a pungent sweat/kitchen odor, also reminiscent of onions with some fruity connotations, and perception thresholds in the pg/l range. It was postulated that the odorless precursors for these compounds are cysteine conjugates. Bacterial isolates obtained from the human axilla and belonging to the Corynebacteria were, indeed, found to have the enzymatic capacity to release various thiols from cysteine conjugates. The metC gene, which is known to code for a cystathione-beta-lyase, was cloned from the axilla isolate Corynebacterium striatum Ax20 and heterologously expressed in E. coli. The pure recombinant enzyme cleaves various cysteine conjugates and has a similar substrate specificity as the cell homogenates of the wild-type. The recombinant enzyme was finally incubated with odorless axilla secretions and shown to release odoriferous thiols.