Catalyzes the cleavage of L-allo-threonine and L-threonine to glycine and acetaldehyde. Can also act on L-erythro-phenylserine, L-threo-phenylserine, L-beta-3,4-methylenedioxyphenylserine and L-beta-3,4-dihydroxyphenylserine. L-threonine = acetaldehyde + glycine L-allo-threonine = acetaldehyde + glycine Optimum pH is 8.0-8.5. Optimum temperature is 25 degrees Celsius. Homotetramer. Belongs to the threonine aldolase family.