Milk xanthine oxidase exhibits a broad substrate specificity that includes purines, aldehydes, and pteridines (1). The mechanism of substrate oxidation, particularly that of purines, has been the subject of several studies (2-4). The present report concerns the observation of a new class of substrates, quaternary heterocyclic compounds, which are oxidized at pH values above 9.6. A partial list ...

1. The results are presented of a cross-sectional study of 25 non-pregnant and 125 pregnant/postnatal women in whom platelet angiotensin II binding and plasma angiotensin II, plasma renin concentration and plasma renin substrate were measured. 2. Platelet angiotensin II binding was significantly lower in the first-trimester patients as compared with the non-pregnant women (P less than 0.001). S...

Tension outputs were measured in skinned crayfish muscle fibers exposed to solutions variously buffered for both Mg-adenosine triphosphate (ATP) and Ca. Two types of data are shown, relating tension and substrate concentration with different levels of Ca present, or tension and calcium concentration at different levels of substrate. The data are fitted by curves calculated from a general equati...