Enzyme defect tested in Guthrie's test?

Ans. is 'a' i.e., Phenyl alanine hydroxylase* Guthrie's test is done to detect Phenylketonuria. Phenylketonuria is caused by a defect of phenylalanine hydroxylase.* It was devised by Dr Robert Guthrie after the birth of his own child with PKU.* It is based on the fact that an organism Bacillus subtilis needs phenyl ketone for its growth.* A small drop of blood is taken from the heel of a newborn and applied to a card. A punch-out dried disc from the card is then incubated on a petri dish plated with bacteria (Bacillus subtilis) in the presence of a growth inhibitor, B-2-thienyl-alanine. High levels of phenyl ketone in the blood sample overcome the inhibition, and allow the bacteria to grow. So, a colony count of the plate will give us an approximate concentration of phenyl ketone inthe blood.* However, this test has been replaced by HPLC with Tandem Mass spectrometry