Inhibition of alkaline phosphatase by oestradiol phosphates.

specific biological activity when isolated from different species may differ chemically. The haemo. globins are an example of this (Porter & Sanger, 1948), and it is clear that some variation in structure may occur in such a series of compounds without the specific action being greatly modified. From solubility studies, Desreux & Herriott (1939) postulated the existence of at least two components in swine pepsin, both of which possess enzymic activity. It is probable that the duality of ox ribonuclease is a similar phenomenon. As a similar composition was found for a number ofpreparations made from small numbers of pancreases obtained. over 12 months from different slaughter houses, it would seem that the two forms exist together rather than that individual animals have wholly one or the other type. The structural differences which alter the chromatographic behaviour have not yet been investigated and may well be subtle enough to escape detection by the technique at present available. From the aspect of protein structure these results would appear to give support to the idea of the existence of families of nearly identical proteins (cf. Synge, 1950).