Enzyme catalyzed hydrolysis of inorganic pyrophosphate. Current view of problems in characterization of PP1-phosphohydrolytic activity associated with alkaline phosphatases (EC 3.1.3.1).

A survey of the hydrolytic activity of alkaline phosphatase (EC 3.1.3.1) reveals that PP1, like phosphomonoesters, can serve as substrate in vitro. This pp1-phosphohydrolytic activity can be distinguished from PP1-phosphohydrolytic activities of inorganic pyrophosphatases (EC 3.6.1.1) and glucose-6-phosphatase (EC 3.1.3.9) by several criteria. Discrimination among these hydrolytic enzymes is possible by their dependence on variation of pH and of magnesium to PP1 ratios in the assay solutions. The true substrates and modifiers are not simply PP1 and magnesium, but the equilibrium species in mixtures of these two. The physiological significance of each of the three enzymes is not predictable from their differential efficiency as catalysts of PP1-hydrolysis in vitro.     

Thiocyanate ion formation in rapeseed meals.

Meal prepared from unheated rapeseed (Brassica napus cv. Zephyr) showed the presence of t,iocyanate ion, while meal from heated seed of the same cultivar did not show detectable amounts. Unheated seed meal on autolysis, and heated seed meal on incubation with thioglucosidase, yielded increased amounts of thiocyanate ion. Various commercial rapeseed meals showed the presence of t,iocyanate ion only after enzyme incubation. Low glucosinolate, cv. Bronowski, and higher glucosinolate, cv. Zephyr on enzymic incubation yielded comparable amounts of thiocyanate ion, suggesting that the precursor responsible in the two varieties was the same and present in similar quantities. No formation of thiocyanate ion was observed on incubation of sinigrin with thioglucosidase. Rats dosed with heated meal, containing intact glucosinolate, showed a slight increase of thiocyanate ion in the urine as compared with control rats dosed with water, while a relatively large increase followed dosing with sinigrin. Rats dosed with meal containing free thiocyanate ion excreted the ingested thiocyanate ion almost quantitatively.