Saturated acyl-enzyme formation causes

Freeing of PAN-SH site  In fatty acid synthesis After priming reactions (first two reactions) Acyl - malonyl - enzyme is formed Central thiol (4-phosphopantetheine -SH group or Pan - SH group) of ACP is covalently linked with malonyl group Peripheral thiol (cysteine -SH group) of 3-ketoacyl synthase is covalently linked to the acetyl group During elongation steps The acetyl group attached to peripheral thiol (cysteine -SH) is transferred to the malonyl group bound to central thiol (Pan -SH group). Simultaneously 1 CO2 is liberated from malonyl group. Thus:- Central thiol (Pan -SH) contains 4 carbon atoms residue Peripheral thiol (cysteine -SH group) becomes free After elongation steps Saturated acyl-enzyme is formed 4 carbon unit (butyryl) is transferred from central thiol (Pan -SH) to peripheral thiol (cysteine -SH group). Thus:- Central thiol (Pan -SH) becomes free to accept new malonyl for next cycle Peripheral thiol (cysteine -SH group) contains 4 carbon unit