Can I use a 1password 5 for mac license in 1password 4.4.3 for mac version.
If not, how can I buy the specific license.
The license file for version 5 is identical to the one for version 4, so you can just apply it to 4.4.3.
hawkmoth is quite correct If you were to purchase a 1Password 5 for Mac licence you are licensed to run 1Password 3 through to 5. If version 4 is the latest you can run right now you can do that, knowing if you upgrade to Yosemite later the licence still covers 1Password 5.
If you have any more questions do please ask.