An old puzzle in protein biochemistry concerns the ready conversion of ovalbumin, by proteolysis, to the much more stable derivative, plakalbumin. Ovalbumin is now known to belong to the serpin superfamily, most of which are serine proteinase inhibitors. We report here studies of two such members of the family, the human plasma proteins alpha 1-antitrypsin and antithrombin, and show that they undergo a similar change in stability on selective proteolysis. This change, which is accompanied by a loss of inhibitory activity, can best be considered as an irreversible molecular transition from a native stressed (S) conformation, to a more ordered relaxed (R) form. The maintenance of the native S conformation, and hence the maintenance of inhibitory activity, is critically dependent on the integrity of an exposed loop of polypeptide. We propose that the susceptibility of this peptide loop to proteolytic cleavage gives it an incidental role as a physiological switch which allows the inactivation of individual inhibitors by specific proteolysis. The vulnerability of this exposed loop in each inhibitor also explains the pathological action of a number of venoms and toxins. In particular, the demonstration here of the cleavage of antithrombin, by leukocyte elastase, explains an observed change in blood coagulation that accompanies severe inflammation and which can result in fatal thrombosis.

Animals↗

PubMedDate not supplied

Reactivity of the beta-93 SH groups in Hb Köln.

The beta-93 SH groups were found to be present in freshly purified Hb Köln, but over a period of several days storage they gradually oxidized to form inter-beta chain disulfide bonds. It is suggested that this gradual oxidation accounts for the low SH values which have been reported. The SH groups of Hb Köln were also found to react more readily than normal with H2O2 and O2-.

Blood Preservation↗

PubMedDate not supplied

The unstable hemoglobins.

The hemoglobin variants have a range of stabilities, a number being sufficiently unstable to cause a hemolytic anemia in the heterozygote. These unstable hemoglobins can be readily detected by standard stability tests. The abnormalities in the unstable hemoglobins result in an increased molecular flexibility that affects both the globin chain and the hemoglobin tetramer. The unstable globins are generally synthesized at a normal rate but their distorted structure leads to proteolytic destruction, primarily in the bone marrow. This explains why they are always present in much reduced amounts in the circulation. Evidence from the unstable hemoglobins is that overall globin synthesis at the cellular level continues until there is compensation for the loss of the abnormal chain. Increased flexibility or distortion of the hemoglobin molecule allows more ready oxidation to methemoglobin but, more importantly, there is also rapid conversion of methemoglobin to hemichrome with resultant denaturation and precipitation. The process is accompanied by the release of activated oxygen but there is no evidence that the amounts formed are sufficient to give cell damage. Hemolysis primarily occurs in the microcirculation due to the mechanical obstruction produced by the rigid Heinz bodies.

1-Propanol↗