Julian Overnell

Characterisation of cadmium-binding proteins from mussels, Mytilus edulis (L), exposed to cadmium

Three Cd2+-binding proteins have been purified and partially characterised from the digestive gland of the bivalve mollusc, Mytilus edulis, after exposure to Cd2+. The major protein, which was judged to be pure on polyacrylamide gel electrophoresis, showed many of the characteristics of mammalian metallothionein; having a high -SH content, few aromatic amino acids and a high A250/A280 nm ratio which disappears on acidification. It also contains Zn and Cu, but differs in its higher apparent molecular weight of about 25 000 and high glycine content (12-19%). The two additional Cd2+-binding proteins had lower cysteine contents and different molar proportions of Cd2+, Zn2+ and Cu2+.

Evidence for the natural occurance of (cadmium, copper)-metallothionein in the crab Cancer pagurus

Abstract 1. The presence of high cadmium in crabs, Cancer pagurus, from Orkney and Shetland has been confirmed. The mean value for cadmium in these crabs is about 3 times higher than those from Devon and Aberdeen, but the peak values are about 5 times higher. 2. A low molecular weight, heat-stable, cadmium and copper binding protein having the characteristics of metallothionein has been isolated from the hepatopancreas of wild specimens of the crab, Cancer pagurus. 3. Induction of metallothionein was achieved both by feeding with cadmium treated mussels and by injection. 4. The major product isolated showed a pair of bands on gel electrophoresis. They were designated metallothionein II-A and II-B and had apparent molecular weights of approx 10,000–11,000. The cysteine content was 30 mol% and the molar ratios of cadmium, copper and zinc were 49:49:2. The sulphydryl to cadmium ratio was 3.

Characterization of two molecular weight classes of cadmium binding proteins from the mussel, mytilus edulis (l.)

Inducible cadmium binding proteins (Cd-BP) in the mussel, Mytilus edulis, were resolved into two molecular weight components by gel permeation chromatography on Sephadex G-75. Each of these two molecular weight components was further resolved into four subcomponents by DEAE ion exchange chromatography. All eight subcomponents bound cadmium and exhibited significant u.v. absorption at 254 and little absorption at 280 nm. Based on amino acid composition analysis two classes of proteins were identified, one having higher cysteine (approximately 25 mole %) and lower serine and glutamic acid contents compared to the other class.

The effect of some heavy metal ions on photosynthesis in a freshwater alga

Abstract The effect of the following metals: copper, cadmium, lead, mercury, methyl mercury, and thallium, and the herbicide 3(3,4-dichlorophenyl)1,1-dimethylurea on (a) the light-induced oxygen evolution, (b) the Hill reaction (water → dichlorophenol-indophenol), and (c) a modified Mehler reaction (dichlorophenol-indophenol → methyl viologen) was studied with the freshwater alga Chlamydomonas reinhardii . The light-induced oxygen evolution of whole cells was found to be very sensitive to the cadmium ion, but this ion was almost without effect on the Hill reaction and the modified Mehler reaction. The light-induced oxygen evolution was also very sensitive to methyl mercury and lead.

Copper metabolism in crabs and metallothionein: In vivo effects of copperII on soluble hepatopancreas metal binding components in the crab Cancer pagurus containing varying amounts of cadmium

Abstract 1. 1. Injection of low cadmium crabs with copper II gives rise to soluble polydisperse copper-containing components whose size distribution changes with time. 2. 2. Short-term exposure of crabs, containing cadmium metallothionein, to copper II gives two possible metal distributions depending on the original cadmium level. (a) Low cadmium level—cadmium is displaced from metallothionein to high molecular weight components, (b) high cadmium level—a mixed (cadmium, copper)-metallothionein is produced. 3. 3. Analysis of an isolated (cadmium, copper)-metallothionein suggests a copper-bound cysteine to copper molar ratio of about 1.4:1.

Use of 2-mercaptoethanol during chromatography of crab (Cancer pagurus) metallothionein on deae cellulose

The chromatographic properties of crab metallothionein appear particularly sensitive to oxidation, and this oxidation does not take place when 2-mercaptoethanol is present in the buffers. The chromatographic changes brought about by oxidation can be reversed by subsequent addition of 2-mercaptoethanol.

A method for the isolation of metallothionein from the hepatopancreas of the crab Cancer pagurus that minimizes the effect of the tissue proteases

Abstract 1. 1. Use of an initial batch DEAE cellulose chromatography in one step separates metallothionein from all measurable protease activity. 2. 2. The product obtained shows significant differences from that obtained earlier using a heat treatment step.

The partition of copper and cadmium between different charge-forms of metallothionein in the digestive tubules of the crab, Cancer pagurus

In the presence of 2-mercaptoethanol DEAE cellulose chromatography of desalted hepatopancreas cytosols of crabs rich in both copper and cadmium yielded three peaks, probably all due to metallothioneins, with very different copper to cadmium ratios. Addition of a copper glycine complex to a desalted crab cytosol containing cadmium metallothionein gave a chromatogram similar to that obtained by in vivo administration of copper and cadmium. The chromatographic distribution of the metals between the different charge-forms in the distal and proximal portions of the tubules was basically similar although the concentrations of the metals were different.