Purification and Characterization of Three Polyphenol Oxidase Isozymes From Lobster (Homarus Americanus)

Abstract

n r e e isozymes of polphenol o x i h e (PPO I , PPO 11 and PPO Ill) were purified from lobster (Homarus americanus) by ion-exchange chromatography and preparative isoelectric focusing using a Rotofor cell. The purwed isozymes migrated as single protein bands in polyacrylamide gels with Ri values corresponding to molecular weights of 32,180,35,480 and 39,300, respectively. 7he p l values of the PPO isozymes were 3.89, 4.26 and 4.54, respectively. PPO I was most active at pH 6.5 and most stable from pH 6.0 to 7.0; PPO 11 was most active within the pH range 6.0 to 7.0, and most stable within the pH range 4.0 to 9.0; while PPO Ill was most active at pH 7.0 and most stable in the pH range 6.0 to 8.0. The temperature optimum for the PPO-dihydroxyphenylalanine oxidation reaction was 35C with PPO I and 45C with PPO 11 or Ill. Lobster PPO I lost about 30% of its initial activity after 30 min incubation at 45C, while PPO I1 and I1 retained virtually all their activity afrer the same heat treatment. The catalytic specijcities of the PPO isozymes were relatively higher with dihydroxyphenylalanine as substrate than with chlorogenic acid.

Phenoloxidase Activity of Hemocyanin in Whiteleg Shrimp Penaeus vannamei: Conversion, Characterization of Catalytic Properties, and Role in Postmortem Melanosis

“…The optimal temperature of HcPO in whiteleg shrimp is ∼45 °C (data not shown). The optimal temperature is comparable to that in P. japonicus (4), P. monodon PO ( 13), H. americanus isoenzymes II and III PO (32), P. duodarum, and P. setiferus PO (14). In a similar way, optimal pH is 7.6 (data not shown), similar to that for PO in P. duodarum, P. setiferus (14), and Panulirus cygnus (33).…”