An enzymatic assay for the cyanide contents of cassava parenchymal tissue (peeled root), cassava peel or cassava leaves is described. The material is homogenised in orthophosphoric acid; filtered through glass-fibre paper and aliquots of the filtrate are neutralised and incubated with exogenous linamarase for 15 min. The cyanogenic glucosides present are hydrolysed to free cyanide which is estimated spectrophotometrically. The acid extraction solution inactivates endogenous linamarase, and assay of aliquots without enzyme treatment gives the free (non-glycosidic) cyanide contents of the extracts. The acid extracts are stable for at least 4 days at 4"C, and the steamdistillation/aspiration of earlier methods is unnecessary. The detection limit is < 0.01 mg(O.l parts cyanide per lOOg fresh weight and peeled root,and40-50 samplesper day can be handled easily. Analyses of eight cultivars indicated longitudinal and radial cyanide gradients in the roots, and the problem of sampling bulky roots is discussed.

No abstract

The changes in concentration of free cyanide (non-glycosidic) and bound cyanide (cyanogenic glucosides) in fresh cassava chips during dehydration, boiling or soaking in water were studied. All of these processes rapidly removed free cyanide from the chips, but only 8-1 2% of the total cyanide is present as free cyanide. Air-drying at four different temperatures showed that 29% of the bound cyanide was removed by drying at 46.5"C; smaller losses were recorded at the higher temperatures. Boiling chips for 25 min removed 55% of the bound cyanide, all of which could be accounted for in the boiling water. Stirring in cold water was ineffective (< 5% loss after 4 hr) for short periods, but cyanide losses increased after longer periods (50% loss after 18 hr) probably because of the onset of fermentation. These decreases in total cyanide content are smaller than indicated by earlier workers.

1. Large quantities of human Factor XIII were prepared from ethanol precipitates of outdated human plasma. 2. Material homogeneous after chromatography on DEAE-cellulose was further resolved into two proteins, A and B, after filtration on Sepharose 6B. 3. Protein A has a molecular weight of 350000 and a subunit structure a(2)b(2) and is activated by thrombin and calcium. Protein B is inactive and probably has a subunit structure b(2). 4. Calcium causes protein A, after thrombin cleavage, to fragment to give protein B and a protein, containing only a' subunits, which is catalytically active. The latter protein slowly forms a misty precipitate which is still active and not cross-linked covalently. This confirms the suggestion of Schwartz et al. (1971) that catalytic activity is only associated with a' subunits. 5. Iodoacetate, which inhibits the enzyme, does not inhibit dissociation and aggregation of protein A. 6. The existence of two proteins and the fragmentation are possible explanations for the wide range of molecular weights given for Factor XIII in the literature.

1. A continuous fluorimetric assay for blood-clotting Factor XIII based on the incorporation of dansylcadaverine into casein was investigated. 2. Hammarsten casein was fractionated to yield the beta-casein, which was dephosphorylated and acetylated to give a substrate which itself did not bind calcium and which was not cross-linked by the activated Factor. 3. The modified beta-casein was used as substrate for a continuous fluorimetric assay and as substrate for the incorporation of radioactive glycine ethylester. 4. A linked fluorimetric assay for the zymogen is described. 5. The K(m) for calcium was redetermined and at 0.2mm was in the physiological range and much lower than the values reported by others using substrates which interact with calcium. 6. The K(m) for casein is about 14mum.