这个chemical messenger 是在这里定位 function by activating the enzymes that release these other, more specific chemical messengers from the cell wall.
that 后面的内容指的是enzymes而不是, 然后Oligosaccharins are fragments of the cell wall released by enzymes 这句表明Oligosaccharins是由enzymes释放的,这两句结合就是指oligosaccharins是chemical messengers的一种