Some biological interactions studied by pulse radiolysis techniques.

Complex formation betwel'n proteins and ùrug ' , mLLco-poly,;accharide;, an1l dyes, or detergent typc molecules is well documentcd in tbc litcraturc ( 1•3) and has been studied b y a varicty of methods including ultrafiltration , dialysis and metachromatic spcctrometry. In this romrnunication we attempt to show that thesl' binding procc ses can be gcnerally investigated by pulsc radiolysis which , in 1>ome cases, providcs information not obtainablc by oth cr methods. For the particular example of penicillin binding to proteins (~) we hav<· measurcd tbc variation in the reaction rate of e~ with proteins (e.g. bovini' serum albumin [BSA] or lysozyme) alone, and wh en complcxed witb penicillin G [P en G]. Tbc logic of tbc method can be underslood from tbc data prescntcd in Fig. l. Curve a rcpresents the change in firs t order rate cons tant of er elative to the conccntration of P en G. With the same con· a q centrations of Pen G, in tbc presence of 10 5 M BSA, curve b is obtained . Curve cis the expected cbange in rate constant if the BSA and Pcn G reacteù inùcpcndently with e~ and no interaction between thc two components took piace. By subtraction of curve a from curve b one obtain curve d which shows a progressive decrease in r eactivity <>f BSA towards c~ when complexed ·with increasing amounts of P en G. The fact that the reactivity of BSA-Pen G complex (curve b) is lcss than the expectrcl additive function (curve c) indicates some kind of intcraction h etwcen the two comp01wnts.