No professional service corporation organized under this chapter shall engage in any business other than the rendering of the professional services for which it was incorporated or service as a trustee as authorized by RCW
11.36.021 or as a personal representative as authorized by RCW
11.36.010: PROVIDED, That nothing in this chapter or in any other provisions of existing law applicable to corporations shall be interpreted to prohibit such corporation from investing its funds in real estate, personal property, mortgages, stocks, bonds, insurance, or any other type of investments.