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(Bourdieu, 2004).

The complement of enzyme activities of a selection of commercial protease preparations were determined using fluorogenic substrates. Alcalase was used in combination with other commercial enzyme preparations to produce cod muscle (Gadus morhua) hydrolysates. Each muscle hydrolysate was characterized with respect to the percentage degree of hydrolysis (DH %), peptide molecular weight range, and free amino acid content. The enzyme preparations containing predominantly protease or endopeptidase activities achieved high DH % and produced significant amounts of peptides below a molecular weight of 3000. Alcalase combined with exopeptidase-rich preparations produced hydrolysates rich in low-molecular-weight peptides. Selecting combinations of enzyme preparations with complementary activity profiles could be used to manipulate the peptide molecular weight profile of hydrolysates.

Uiuversily ol' Plymouth. Drake Circus, Plymouth. PL4 8AA Higher plants and at lcast some yeasts, freshwater algae and marine diatoms respond to exposure to the toxic non essential heavy metal cadmium by synthesising glutathione-derived peptides with a high affinity for cadmium and some other heavy metals [ 1 -61. These peptides have the general formula gamm[EC]nG where n = 2 to 11 and are given the trivial name phytochelatins (PC) (if of plant origin) or cadystins (if derived from yeasts). Synthesis of these heavy metal chelating peptides is catalysed by the metal activated phytochelatin synthetase using substrate derived from the intracellular glutathione pool 1.31. The efficiency of metals as activators of phytochelatin synthetase varies with species but generally follows the sequence Cd2%u2%Zn2+ which is similar to the relative affinities of phytochelatins for the same ions [3]. Whereas sequestration of cadmium is a detoxification mechanism involving transport of Cd:PC complexes into vacuoles, the intracellular fate of Cu:PC and 2n:PC complexes is less clear. Formation of PC complexes with essential heavy metals may be [part ofl a metal homeostasis mechanism, with FC acting as a "chelation buffer". The role of PC in enabling plants to deal with toxic levels of essential heavy metals is not known but there is evidence that PC synthesis is not a primary response of plants to toxic levels of&+ or ZI?+ [41. Marine diatoms have been shown to have a good correlation between F C synthesis and normal environmental levels of cadmium [5.6]. In contrast, little is known about the situation in marine macroalgae. even though these species have been used as environmental biomonitoring organisms for some time 171. Past mining activities in the South West of England have resulted in areas of chronic heavy metal contamination of rivers, estuaries and coastal regions. The ubiquitous presence of species such as Fitcus vesiculosus and Ulva lacruca in both clean and contaminated sites provides an opportunity to investigate their biochemical responses to natural and laboratory exposure to heavy metals and to examine detoxification and tolerance mechanisms. This report concentrates on establishing the effects of exposing the above species to cadmium and copper under laboratory conditions. Fucus vesiculosus and Ulva laciuca were obtained from uncontaminated local sites, washed in clean artificial seawater [Instant Ocean, J & K Aquatics Ltd.]. kept in tanks of clean aerated artificial seawater for two weeks and then in artificial seawater containing CdSO4 [0.4 mg.l-I] (Fucus) or CuSO4 [O -0.92nig.l-I] (Ulva) for 1 week. Samples 14 grams] of algae were blotted dry, frozen in liquid nitrogen. ground in mortars and then extracted in 50mM pH 7.5 Tris/HCI buffer [Buffer A] (2cm3 buffer per gram tissue). Extracts were filtered through muslin and filtrates were clarified by centrifugation in a microcentrifuge [2 min. X 13,oOOgl.For metal-binding peptide purification, extracts of Fucus were applied to a column (2.5 X 1.5 cm) of QAE cellulo...

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