Molecular weight and shape of angiotensin-I converting enzyme. A neutron scattering study.

The molecular weight of angiotensin-I converting enzyme from pig lung has been determined to be 112000 (+/- 6000) by neutron scattering. This is somewhat lower than the value determined by SDS-PAGE and than previous estimates which, however, show a very wide range of values. A quantitative analysis of the amino acid and carbohydrate content was made in order to determine the enzyme concentration. The small angle neutron scattering technique also gives information on the molecular shape, yielding a radius of gyration of 44.5 +/- 1.5 A which, for the observed molecular weight, indicates that the angiotensin converting enzyme molecule is clearly elongated in aqueous solution. Dynamic light scattering experiments confirm this conclusion.