Stopped-flow x-ray scattering: the dissociation of aspartate transcarbamylase.

Abstract
A combination of stopped-flow and X-ray scattering techniques was used to study the dissociation of aspartate transcarbamylase (carbamoylphosphate:L-aspartate carbamoyltransferase, EC 2.1.3.2) with a 2:1 excess of p-chloromercuribenzenesulfonic acid (the ratio being calculated on a basis of reactive sites), in the presence and absence of the transition state analogue N-(phosphonacetyl)-L-aspartate. At 10 mg of protein/ml, the scattering curves allowed some details of the reaction to be followed with a time resolution down to 1 s. The curves showed not only the dissociation of the enzyme complex but also the formation of the subunits. With present facilities, X-ray scattering could be used to study dissociation or reassociation reactions with a time resolution of the order of 100 ms.