Mapping database identifiers https://www.uniprot.org/help/api_idmapping

MappingProgram.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Net;
using System.Text;

public class MappingExample
{
	private const string UniprotServer = "https://www.uniprot.org/";

	static void Main()
	{
		Run("uploadlists", new[] {
				new KeyValuePair<string, string>("from", "ACC"),
				new KeyValuePair<string, string>("to", "P_REFSEQ_AC"),
				new KeyValuePair<string, string>("format", "tab"),
				new KeyValuePair<string, string>("query", "P13368 P20806 Q9UM73 P97793 Q17192")
			});
	}

	private static void Run(string tool, KeyValuePair<string, string>[] parameters)
	{
		StringBuilder locationBuilder = new StringBuilder(UniprotServer + tool + "/?");
		for (int i = 0; i < parameters.Length; i++)
		{
			if (i > 0) locationBuilder.Append('&');
			locationBuilder.Append(parameters[i].Key).Append('=').Append(parameters[i].Value);
		}
		string location = locationBuilder.ToString();

		HttpWebRequest request = (HttpWebRequest)WebRequest.Create(location);

		// Set some reasonable limits on resources used by this request
		request.MaximumAutomaticRedirections = 4;
		request.MaximumResponseHeadersLength = 4;

		// Set credentials to use for this request. Highly not recommended by Uniprot
		request.Credentials = CredentialCache.DefaultCredentials;

		HttpWebResponse response = (HttpWebResponse)request.GetResponse();
		if (response.StatusCode == HttpStatusCode.OK)
		{
			Console.WriteLine("Content length is {0}", response.ContentLength);
			Console.WriteLine("Content type is {0}", response.ContentType);
			Stream receiveStream = response.GetResponseStream();
			if (receiveStream == null)
			{
				Console.Error.WriteLine("The Response Stream is empty");
				return;
			}
			// Pipes the stream to a higher level stream reader with the required encoding format. 
			using (StreamReader readStream = new StreamReader(receiveStream, Encoding.UTF8))
			{
				Console.WriteLine("Response stream received.");
				Console.WriteLine(readStream.ReadToEnd());
			}
		}
		else
		{
			Console.Error.WriteLine($"Status code is not ok: {response.StatusCode}");
			return;
		}
		response.Close();
	}
}