Extraction of Spartan apple (Malus domestica) fruit acetone powder and fractionation of the extract on DEAE‐agarose allowed detection and quantification of 10 glycosidases active toward 4‐methylumbelliferyl glycosides. Hydrolysis was measured fluorimetrically. The predominant activity, a β‐d‐galactosidase (EC 3.2.1.23), labile upon purification, was stabilized by soluble PVP. Molecular weights, measured by gel permeation HPLC, pH optima and Km values were obtained for most glycosidase activities. Multiple forms of several activities were found. The major α‐d‐ and β‐d‐galactosidases were resolved on phosphocellulose. The β‐d‐galactosidase so obtained had associated α‐l‐arabinopyranosidase and β‐d‐fucosidase activities which were retained upon GP‐HPLC. Mixed substrate kinetic analysis and inhibition analysis of this fraction indicated that the enzyme has 3 catalytic sites, 1 for each substrate, whose substrates mutually influence each other's activity positively.

No abstract

No 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.

No abstract