Why do you use NaOH to lyse cells and what's the function of...

To use NaOH to lyse cell wall: a-glucan and some forms of b-glucan of the yeast cell wall are soluble under alkaline conditions.

The function of beta-mercaptoethanol: reducing agents, such as dithiothreitol or b-mercaptoethanol are needed because the breakage of disulphide bridges between mannose residues and wall proteins is necessary for appropriate exposition of the inner glucan layer.

References:

1. Horvath A, Riezman H. 1994. Rapid protein extraction from Saccharomyces cerevisiae. Yeast 10: 1305–1310

2. Zhang T, et al. 2011. An improved method for whole protein extraction from yeast Saccharomyces cerevisiae. Yeast. 28(11):795-8