Unless you are running Windows 10 Pro or any other enterprise variant, such as Windows 10 Enterprise or Windows 10 Education you can not disable Windows Defender.
If you are running another antivirus Windows Defender should disable itself, this is a default action performed when another antivirus is installed.
The culprit for this high CPU usage is the Antimalware Service Executable, (there is no relation between this and Malwarebytes Antimalware). The main problem here is the process called Antimalware Service Executable and its corresponding file msmpeng.exe., this is part of Windows Defender. There is a very good explanation and several suggested means of resolving this problem which you can find at Emsisoft's website. This should help you to understand why this is occurring and how to resolve it.
If this does not resolve this issue malware could be responsible. If this is the case you will need to run security scans to find and remove the malware. If this is the case your topic will need to be moved to the Am I Infected, What Do I Do forum. These scans may not be run in the Windows forums. If this is the case I will request that this topic be moved and provide you with instructions to run these scans.
Just for clarification purposes please do the following.
Please download Security Check by Screen317.
Double click on the download and choose to run the program.
A screen similar to the one below will open, click any key to run the program.
When the scan is finished there will be a log, copy and then paste the log in your next post.