The boss of ISR Capital - one of the firms caught up in the fallout from the 2013 penny stock crash - has quit.

Ms Quah Su-Yin stepped down as chief executive and executive director of the investment firm last Saturday, according to a Singapore Exchange (SGX) filing yesterday.

It said she was leaving to focus on the family business.

She is the sister of Ms Quah Su-Ling, former CEO of Ipco International.

Ms Quah Su-Ling was arrested on Nov 24 last year in relation to the penny stock crash of shares of Asiasons, LionGold and Blumont Group.

On Nov 24, ISR Capital shares plunged from 28.5 cents to 12.7 cents, prompting an SGX query which led to a trading halt request and eventual suspension on Nov 27.

A week after the suspension, Ms Quah Su-Yin said that "inaccurate media reports" had implied links between the company and a probe by Singapore regulators into the penny stock crash, leading to ISR Capital's stock volatility.

She said in a filing to the SGX on Dec 1 that "there is no direct or indirect link of ISR Capital Limited, its directors and officers" to the penny stock probe, "save for the fact that I am the sister of one of the three co-accused charged on Nov 25, 2016".

ISR Capital appointed Mr Lee Ka Shao - a veteran investment banker who was managing director of central treasury in DBS Bank - as an independent non-executive director yesterday.

Mr Lee said in a statement that his appointment "is to safeguard and protect the interest of the minority shareholders who may have been caught in a bind, especially with (ISR Capital's) recent stock trading suspension".

He said he would help to work with all stakeholders to "achieve a desirable outcome as to the continuity and future of ISR Capital Limited's operations and plans".