Pseudo-catalase

The dinuclear units are closely related to the dinuclear Mn units believed to be present at the active site of manganese (pseudo)catalases. 7 This view is supported by the previously reported biomimetic (catalytic) activity of 1 (see also below). 

In this study we nave further investigated the pseudo catalase activity both in relation to catalase and to different photosystem II functions. 

Unwashed thylakoids showed a catalase activity as high as 400 fjoaol O /mg Chlxh (Fig 1). Most of this activity (98 %) could be removed by 7 washes. The thylakoids also showed a KCN-insensitive, pseudo catalase, activity. This activity was, however, not affected by the washing procedure. An activity of 13 pmol 02/mg Chlxh was found throughout the 7 washes. This clearly Indicates two different pools of H2O2 decomposing agents. One that is very sensitive to KCN and loosely bound to the thylakoids and one that is sensitive to KCN and closely associated with the thylakoids. 

Fig.l Wash treatment of thylakoids Catalase activity (Oimmmo), Pseudo catalase activity 100 stnd the ratio... 

The pseudo catalase activity was found to be coenriched with the photosynthetic oxygen evolution when PS II particles were isolated from washed thylakoids (not shown)... 

Fig. 2 Heat treatment of PS II enriched particles, Photo-synthetic oxygen evolution r Pseudo catalase activity...

Thus the pseudo catalase activity appears to be closely connected to PS II. To further localize the pseudo catalase activity, PS II particles were subjected to selective inhibition treatments. 

Another selective inhibitor of the oxygen evolving complex is NH2OH. Treating PS II particles with NH OH (Fig 3) effectively inhibited the oxygen evolution and the water to DCIP reaction. The treatment also resulted in an almost complete (97 %) loss of Mn. The release of Mn correlated well to the inhibition of oxygen evolution and water to DCIP reaction. In contrast, the pseudo catalase activity was only inhibited to some 60 % and was not at all correlated to the release of Mn. Thus, the pseudo catalase activity is not dependent, on either bound or free, Mn. 

Most lactic acid bacteria tolerate the presence of oxygen but do not use it in energy-producing mechanisms. Depending on the species, they use different pathways to eliminate the toxic peroxide, activating peroxidases which use NADH as a reducer a superoxide dismutase, a pseudo catalase and sometimes Mn + ions (Desmazeaud and Roissart, 1994). To date, this subject has not been specifically studied for species isolated in wine. 

The nonheme catalases are sometimes referred to as pseudocatalases. However, this is inappropriate since there is nothing pseudo about their catalase activity. They are better described as Mn catalases. Bacteria that lack Mn catalase (either genetically or through inactivation of the enzyme) show decreased viability, suggesting that Mn catalase does, in fact, play a physiological role in the detoxification of H2O2. 

Cyclic and pseudo cyclic photophosphorylation In 100 il the incubation medum contained 10 imol HEPES NaOH buffer pH 7.8,10 jimol sorbitol.. 4 (imol Na phosphate containing 1.4 kBeq 32p 250 units catalase, freshly isolated pea thylakoids (10 pg chlorophyll) and spinach ferredoxin or pig adenodoxin as indcated. After illumination fa 15 min unda white saturating li t, the reaction was stopped and the radoactivity incapaated into the ATP determined. 

Catalase (1.11.1.6) is present (hydrogen peroxide is decomposed by an enzyme containing a heme or porphorin structural group). Catalase-pseudo (an enzyme not containing a... 

Catalase-pseudo (an enzyme not containing a heme structural unit) decomposes hydrogen peroxide to water and oxygen. 

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