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A leaf protein concentrate prepared from the young leaves of the common nettle (Urtica dioica) failed to support normal growth in young rats; supplementation with methionine produced a protein efficiency ratio greater than that of casein. A nettle leaf wholemeal, providing 66% of the dietary protein, supported normal growth in young guinea-pigs, mice and rats. Chicks receiving the whole nettle meal as their sole dietary protein grew at only half the rate of chicks given a standard commercial diet. A nettle meal-induced hypercholesterolaemia in mature guinea-pigs and kidney hypertrophy in mice and guinea-pigs should perhaps be interpreted as a caution against the indiscriminate introduction of nettles into the human diet.

The vanadium bromoperoxidases c a t a l y s e a h a l i d e -a s s i s t e d d i s p r o p o r t i o n a t i o n o f H, O, [1,2] t o y i e l d an i n t e r m e d i a t e t h a t can undergo f u r t h e r o x i d a t i o n t o produce s i n g l e t oxygen o r promote b r o m i n a t i o n o f a s u i t a b l e o r g a n i c s u b s t r a t e . Bromoperoxidases o f t h i s t y p e a r e widespread i n m a r i n e a l g a e [3], p a r t i c u l a r l y t h e r e d a l g a e and brown a l g a e . We have r e p o r t e d r e c e n t l y [4] t h e i s o l a t i o n and c h a r a c t e r i z a t i o n o f t h e vanadium bromoperoxidase f r o m t h e r e d macroalga CoraZZina officinazis. T h i s i s an e x t r e m e l y l a r g e o l i g o m e r i c p r o t e i n o f M r about 740000 c o n s i s t i n g o f p r o b a b l y 12 i d e n t i c a l s u b u n i t s . Nevertheless, t h e enzyme showed a h i g h degree o f t h e r m o s t a b i l i t y r e t a i n i n g a p p r e c i a b l e a c t i v i t y (approx. 50%) a t 60-70°C and w i t h t h e a c t i v i t y r e s t o r e d on re-adjustment t o 25°C. Repeated c y c l e s o f t h i s t r e a t m e n t gave s i m i l a r changes i n a c t i v i t y [4]. Even a t 90°C f o r 20 min some a c t i v i t y was r e t a i n e d b y c e l l e x t r a c t s and a l t h o u g h t h e p u r i f i e d enzyme was i n a c t i v e a f t e r t h i s t r e a t m e n t i n b o t h i n s t a n c e s t h e a c t i v i t y was f u l l y r e s t o r e d o v e r 30 min a t 25°C. The vanadium bromoperoxidase f r o m t h e brown a l g a AscophyZZum nodosum [5] and t h e l i c h e n Xanthoria par+tina [6] were a l s o t o l e r a n t t o 50°C .and, p a r t i c u l a r l y t h e former, r e t a i ned a p p r e c i a b l e a c t i v i t y a t 70°C; however, r e s t o r a t i o n o f a c t i v i t y on r e a d j u s t m e n t t o l o w e r temperature d i d n o t o c c u r w i t h t h e AscophyZZum enzyme and f o r t h e Xanthoria enzyme was n o t i n v e s t i g a t e d . The vanadium bromoperoxidase f r o m a r e d a l g a Cerarniurn ruhrurn was n o t t h e r m o s t a b l e [7]. G e n e r a l l y speaking o n l y a few enzymes o f l o w M r a r e h i g h l y t o l e r a n t o f i n c r e a s e d temperature and e x h i b i t r e v e r s i b l e d e n a t u r a t i o n so t h e o l i g o m e r i c bromoperoxidase f r o m CoraZLina i s n o t a b l e i n t h i s r e s p e c t . The o l i g o m e r i c s t r u c t u r e o f t h e CoraZZina officinalis enzyme was n o t a p p a r e n t l y d i s r u p t e d b y exposure t o 60°C s i n c e enzyme e q u i 1 i b r a t e d t o t h i s temperature and s u b j e c t e d t o non-denaturing PAGE a t 60°C showed t h e same e l e c t r o p h o r e t i c p r o p e r t i e s as r e p o r t e d p r e v i o u s l y f o r t h e enzyme f r o m PAGE s t u d i e s c a r r i e d o u t a t l a b o r a t o r y temperature d u r i n g p r o t e i n c h a r a c t e r i z a t i o n [4]. The a c t i v a t i o n energy f o r response t o temperature o v e r t h e range 2O"C-5O0C ...

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The vanadium-dependent bromoperoxidase from the macroalga Corallina officinalis was immobilised on a cellulose acetate support with retention of approaching 50% of the applied units of activity. The enzyme exhibited high thermal stability and retained activity in repeated use. The immobilised enzyme showed tolerance to organic solvents similar to that of the free enzyme in the case of methanol but differed for acetone and ethanol, and with the latter showed enhanced activity as the % by volume of the solvent was increased.