α‐Amylase inhibitor is presented in maize seeds. It is a protein as indicated by precipitation with ammonium sulfate and trichloroacetic acid, denaturation by heat, digestion with proteases and by dye‐staining. It was purified to homogeneity by ammonium sulfate precipitation and Sephadex G‐75 gel filtration. It had an apparent molecular weight of 29,600 and did not contain any carbohydrate. Its properties differed from those of previously reported α‐amylase inhibitors, since it was active against α‐amylase of maize, produced during germination as well as against Bacillus subtilis α‐amylase. It was also active against α‐amylase from the insects Tribolium castaneum, Sitophilus zeamais and Rhyzopertha dominica, but it was inactive against α‐amylase from human saliva, hog pancreas, Aspergillus oryzae, wheat, rye, barley, triticale, and sorghum. It was stable for 5 min at 96°C at pH 7. Maximal inhibition required at least 10 min of preincubation with the enzyme at pH 6.8 and 257deg;C. Polyacrylamide gel electrophoresis gave three protein bands, but only one was obtained in S.D.S. and mercaptoethanol.

Simultaneous depletion of phenylalanine and tyrosine by phenylalanine ammonia lyase is described in a mutual competitive inhibition model. The enzymes obtained fromSporidiobolus pararoseus andRhodosporidium toruloides were charaterized in terms of stability, optimal reaction parameters and kinetic behaviour. Both enzymes followed Michaelis-Menten kinetics with respect to the two amino acids. However, the enzyme fromRhodosporidium toruloides was inhibited by high tyrosine concentrations.