The others have covered the other sources of capital, so I decided to cover the subordinated debt.
According to the ActEd notes, subordinated debt is: debt issued by an insurer, in which the repayment of debt that is guaranteed only after policyholders’ reasonable expectations have been met.
And the Investopedia on the web says it is a loan that ranks below other loans with regard to claims on assets or earnings.
According to this article: http://www.moneyweb.co.za/news/economy/uncertainty-over-bank-subordinated-debt/, the global banking industry is expecting the implementation of Basel IV regulations (capital requirement regulatory framework for banks, as Solvency II for insurers) and how these regulations will lead to higher capital requirements. In response, South African banks are expected to issue more subordinated debt as a result, but the banks are likely to be cautious as African Bank was placed under curatorship by the Reserve Bank last year.
The article also touches on uncertainties that arose as a result of the curatorship of African Bank. The subordinated debt holders argued that the curatorship does not necessarily mean a bank failure and that the subordination of their instruments not be applied.
It is also interesting to note how the dominant players in the South African banking industry, namely: Nedbank, FirstRand and Standard Bank all raised their spread on their subordinated debt after the collapse of African Bank, reflecting the perception of increased risk.