Conformational Studies on Large Fragments of Bovine Serum Albumin in Relation to the Structure of the Molecule

A model of albumin is proposed which accounts for the behaviour of bovine serum albumin during proteolytic hydrolysis by several enzymes. This model is tested and confirmed by conformational studies on large fragments of albumin at acid and neutral pH by means of optical rotation and hydrogen ion titration. The isolation of some fragments is described. It is suggested that BSA is a compact molecule at neutral pH, while in the F‐configuration it is composed of a compact NH2‐terminal moiety, and a COOH‐terminal part with a loose structure, which is very susceptible to proteolytic cleavage. The N‐F transition can be interpreted as an isomerization of the NH2‐terminal moiety, without loss of helix content, and an unfolding of the COOH‐terminal part in a cooperative process. Some parallelism between acid and neutral transition is demonstrated.