 In this tutorial, we will learn how to search for rear reactions involving specific chemical compounds. Rear uses the KB dictionary of small molecules to describe reaction participants. This allows to search rear, taking into account the synonyms, the charge, and hierarchical classification of chemical compounds. For a start, let's do a simple text search for Palmitate. Here are the reactions we obtain. However, as we can see, many of these reactions do not seem to contain the actual word Palmitate. We will start to explore our results and understand the relationships of these reactions with Palmitate by clicking on Choose Molecule for Palmitate. We see that Palmitate is found in the name or synonyms of several molecules or classes of molecules. For example, the first two results, hexadecanoate and hexadecanoic acid, have Palmitate as one of their synonyms and participate in the same number of reactions. Let's see the reactions for hexadecanoate and we clearly see that our molecule participates in these reactions. If we do the same for the molecule hexadecanoic acid, we see that it does not directly appear as a reaction participant in rear. To understand this, we need to explain a convention used in rear. KB handles all forms of a given chemical compound, for example neutral versus charged, fully versus partially protonated. Each form has its own unique KB identifier and related forms are linked together. Rear, in order to provide non-redundant and chemically balanced reactions, uses those KB entities that describe the form that is the major microspecies at pH 7.3. Hexadecanoate, but not hexadecanoic acid, is used as a reaction participant at pH 7.3. You can find out more about these concepts in our help pages. If we want to exclude cases like the one just explained, we can click this checkbox. Only a subset of the previously identified KBs are reaction participants. Note that hexadecanoic acid has now disappeared from this list. We go back to browsing the rear reactions that have hexadecanoate as a reaction participant. We can click on this link here. You can see that the query box is now filled with a query that includes the KB identifier of hexadecanoate. We could have done the same query by using the advanced search. To do so, we click on advanced search, then on all, we select reaction participants and KB small molecule and start writing palmitate. Once again, don't be surprised if many different names are proposed that at a first glance do not contain the word palmitate. It's just that the query is performed among all names including synonyms and differently charged versions reported in KB. By selecting hexadecanoate and clicking on search, we retrieve the same reactions as before. In the reaction table, if we want additional information on our molecule, we can click on hexadecanoate. A black tooltip appears. We can select to see the description of this molecule in KB. A lot of information is available about our molecule on this KB page including a list of hierarchical relationships with other molecules. For example, we can see that hexadecanoate is a long chain fatty acid anion. We can now search for reactions with this KB identifier and to do this, we go back to the rear home page, paste this KB ID into the simple query box. We get a significant number of rear reactions in our result page. We can see that some of the results still display reactions involving hexadecanoate, which is expected because it is a child of long chain fatty acid anion. This result nicely illustrates the fact that the default search in rear is a hierarchical search. If we search by reaction participant with a KB ID, we will retrieve all the rear reactions that involve this KB molecule or one of its children. It is of course possible to retrieve the rear reaction in which long chain fatty acid anion is mentioned as a reaction participant. To do this, let's use the advanced search. Enter the KB ID we used previously and click on Exact KB Search. By selecting this option, the list of matching reaction becomes a lot shorter and we can see that the query form was changed and it now shows the prefix KB Exact. These reactions involve as a reaction participant the class of compounds, which is labeled in KB as long chain fatty acid anion and in rear with the synonymous term a long chain fatty acid. All the numbers shown in this tutorial will of course change regularly, depending on the evolution of biological knowledge and on progressing biocuration efforts. Never hesitate to contact us if you have any questions or remarks and to look at our help pages and other videos. Thank you very much for your attention.