Transmembrane protein CD36 is considered to bind its distinct ligands such as long-chain fatty acids primarily by recognizing their terminal carboxyl moiety. In this study, we provide evidence that long-chain fatty aldehydes, such as oleic aldehyde, can be recognized by CD36. We suggest that a single aldehyde group may also serve as one of the structural elements recognizable by CD36.

Cluster of differentiation 36 (CD36) is a broadly expressed transmembrane protein that has multiple ligands, including oxidized low-density lipoproteins. We found recently that CD36 is expressed in olfactory sensory neurons and postulated that it plays a role in the detection of distinct odorants in the nasal cavity. To date, however, there have been few examples of attempts to identify CD36-recognizable odorants. In this study, by an in vitro assay using a peptide mimic of the receptor, we provided evidence that CD36 recognizes (Z,Z)-4,7-tridecadienal, an odor-active volatile compound that is known to occur in Katsuobushi (dried, fermented, and smoked skipjack tuna commonly used in Japanese cuisine as a seasoning) and in the preorbital secretion of male oribi. In addition, by comparing the data with those of its related compounds, we provided information on the structural requirements of (Z,Z)-4,7-tridecadienal for recognition by CD36. For instance, we showed that flexible rotation around the C2-C3 bond of the volatile may be of importance in gaining access to CD36. Identification of (Z,Z)-4,7-tridecadienal as the ligand prompts us to hypothesize that CD36 could participate in the control of distinct mammalian behaviors (e.g., food selection) through its ability to recognize specific odorants in the environment.

Volatile compounds with an aldehyde moiety such as (Z)-9-octadecenal are potential ligands for cluster of differentiation 36 (CD36), a transmembrane receptor that has recently been shown to play a role in mammalian olfaction. In this study, by performing an assay using a peptide mimic of human CD36, we aimed to discover additional ligands for the receptor from volatiles containing a single aldehyde group commonly found in human foods. Straight-chain, saturated aliphatic aldehydes with 9-16 carbons exhibited CD36 ligand activities, albeit to varying degrees. Notably, the activities of tridecanal and tetradecanal were higher than that of oleic acid, the most potent ligand among the fatty acids tested. Among the aldehydes other than aliphatic aldehydes, only phenylacetaldehyde showed a weak activity. These findings make a contribution to our knowledge of recognition mechanisms for flavor volatiles in foods with an aldehyde group.

By starting from a diruthenium bis(µ-hydrosulfido) complex [(Cp°RuCl) 2 (µ-SH) 2 ] (1; Cp°) η 5 -C 5 -Me 4 Et), a series of new mixed-metal sulfur clusters containing both noble metals and group 15 metals have been synthesized. Thus, 1 was allowed to react with 1 equiv of MCl 3 (M ) Sb, Bi) to give the trinuclear Ru 2 M clusters [(Cp°RuCl) 2 (µ-SMCl 2 )(µ-SH)] (3a, M ) Sb; 3b, M ) Bi) containing bridging SH and SMCl 2 ligands. Treatment of 3a with 1 equiv of [Pd(PPh 3 ) 4 ] at room temperature gave a mixture of the Ru-Pd-Sb clusters [(Cp°Ru)(Cp°RuCl)(µ-SSbCl 2 ){PdCl(PPh 3 )}(µ 3 -S)(µ-H)] (4), [(Cp°Ru) 2 (SbCl 2 )-{Pd(PPh 3 )} 2 (µ 3 -S) 2 (µ-Cl)] (5), and [(Cp°Ru)(Cp°RuCl){PdCl(PPh 3 )}(SbCl)(µ 3 -S) 2 ] ( 6). An analogous reaction carried out at -5°C gave 4 as the major product. By contrast, isolation of the Bi analogues from the reaction of 3b and [Pd(PPh 3 ) 4 ] was unsuccessful. It was also confirmed that the isolated 4 was treated with 1 equiv of [Pd(PPh 3 ) 4 ] in THF either at 50°C or at room temperature in the presence of triethylamine to give 5, while 4 was converted to 6 upon either warming to 50°C or dehydrochlorination by the use of triethylamine in THF. Cluster 6 was readily transformed into 5 by treatment with [Pd-(PPh 3 ) 4 ] in THF at room temperaure. Structures of the new clusters 3a, 3b, 4, 5, and 6 have been determined by single-crystal X-ray analysis.

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Humans have a strong preference for sugars and fats, and they recognize dishes and sweets rich in sugars and fats as palatable food. Rodents also have a strong preference for sugars and fats. Two-bottle choice tests using sugars and fats have been reported to show not only their high palatability but also a reinforcement effect (1,2). Conditioned place preference (CPP) tests have been widely used to determine the reinforcement effect of a given sample (3).Tastes considered palatable by humans are not limited to sugars and fats. For example, broths, which contain taste components such as flavors and distinctive aromas extracted from plants and animals, are indispensable for enhancing the taste of dishes. Dashi (broth) made from katsuobushi (dried bonito) is a very basic and indispensable element in Japanese cuisine. Although it is not rich in sugars or fats, Japanese cuisine has provided satisfying meals by fully utilizing the unique aroma and taste of katsuodashi (dried bonito broth). Therefore, it is important to re-evaluate the value of Japanese cuisine that provides satisfaction with low calories.Katsuobushi (dried bonito) is made from katsuo (Skipjack tuna, Katsuwonus pelamis) by the following processes: cutting raw katsuo into pieces, boiling-aging, roasting-drying (smoking and drying over a smoking wood fire), molding, mold inoculation, and sun drying. In this process, the intermediate product from the roasting-drying step is called arabushi. Because tar from the roasting-drying step is deposited on the surface of the arabushi, the surface is shaved during the molding step and the powdery shavings are called G powder. The product from the molded arabushi that is subjected to repeated cycles of mold inoculation and sun drying steps is called karebushi. Both arabushi and karebushi are widely marketed as katsuobushi. A hot water extract of shavings of arabushi or karebushi is called katsuodashi (dried bonito broth), an indispensable broth in Japanese cuisine. Other fishes including maguro (yellowfin tuna, Thunnus albacares), goma-saba (spotted mackerel, Scomber australasicus), souda-katsuo (bullet tuna, Auxis rochei), and katakuchi-iwashi (Japanese anchovy, Engraulis japonicus) are processed in similar ways for use in making broths.Kawasaki et al. and Ackroff et al. found a preference for dried bonito broth in two-bottle choice tests using mice (4, 5). Furthermore, Kawasaki et al. performed CPP tests and found a significant reinforcement effect for a dextrin solution containing natural dried bonito broth (BD), but not for a dextrin solution alone (6). In addition, they analyzed taste components in natural Summary Japanese cuisine has provided satisfying meals by fully utilizing the characteristic aroma and taste of katsuodashi (dried bonito broth), though it is not rich in sugars or fats. Katsuodashi is a very basic and indispensable element in Japanese cuisine, and is a hot water extract of katsuobushi (dried bonito). It has been reported that a dextrin solution containing natural dried bonito broth has a si...

Cluster of differentiation 36 (CD36) is a broadly expressed transmembrane receptor that has multiple ligands. It has been found to occur abundantly on the surface of the olfactory epithelium in mice and postulated to play a role in mammalian olfaction. However, there have been no ethological analyses of the mammalian behaviour showing CD36 involvement in the olfactory perception of a distinct odour-active volatile compound. In this study, we aimed to assess whether mammals perceive oleic aldehyde, an odour-active volatile that serves as a potential CD36 ligand, and if so, whether CD36 is involved in the sensing by following measurements using CD36-knockout mice and their wild-type littermates. In a two-bottle choice test, wild-type mice, but not CD36-knockout mice, discriminated a sucrose solution containing oleic aldehyde from the sucrose solution alone. To assess the importance of the olfactory system in the oleic aldehyde perception, we conducted an exploration test where the animals could rely primarily on the odour of test volatiles for recognition. We found that the wild-type, but not CD36-knockout mice, were aware of the compound. Our results provide behavioural evidence that CD36 plays a role in the perception of specific odour-active volatile compounds in the nasal cavity.Chemosensory systems are responsible for the detection of soluble and volatile chemicals. The two chemosensory systems in mammals, gustatory and olfactory systems, distinguish nutritive compounds from harmful ones within the oral and nasal cavities (10). The sense of smell is particularly important for avoiding harmful chemicals in foods prior to ingestion (7). The olfactory perception starts from the binding of odorants to specific G-protein-coupled receptors on olfactory sensory neurons located within the olfactory epithelium of the nasal cavity (5). However, for many odorants, the precise mechanisms of olfactory detection in mammals remain to be studied. Cluster of differentiation 36 (CD36) is a membrane-bound receptor with two transmembrane spans that is produced and expressed by a variety of sites in the body of vertebrates (23). The receptor is involved in lipid binding and uptake within tissues, such as the small intestinal, adipose and muscle tissues (6). CD36 has also been postulated to play roles in the gustatory system. Indeed, CD36 has been shown to mediate the detection of long-chain fatty acids in the oral cavity, driving the consumption of the lipid species in rodents (12, 16). More

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