Positions B12 Research Articles

Kinetics of ligation reactions of rabbit hemoglobin in quaternary R and T states.

Rabbit hemoglobin shows significantly lower affinity for CO than does human hemoglobin (Hb A). The overall ligand combination and dissociation rate constants reveal, however, only small differences between Hb A rabbit Hb; this is mainly due to the fact that beta chains in rabbit hemoglobin determine the kinetics of ligand dissociation and combination. The heme environment in these chains is probably not very different in rabbit Hb and human Hb A. Rabbit hemoglobin alpha chains, on the other hand, exhibit greatly reduced CO and O2 combination rates in the R state and are primarily responsible for the overall low CO affinity of rabbit Hb. We postulate that the low ligand affinity of alpha chains in rabbit Hb is due to the substitution of larger residues at positions B10(Leu leads to Val), Cd6(Leu leads to Phe), and CD7(Ser leads to Thr). The possible implication of such substitutions for the kinetic and equilibrium properties of rabbit Hb are discussed.

Structure and activity of insulin, XVI. Semisyntheses of desheptapeptide-(B24--30)- up to destripeptide-(B28--30)-insulin with lysine or alanine in place of arginine in position B22: influence on the three-step-increase of activity in positions B24--26 (Phe-Phe-Tyr).

The desonapeptide-(B22--30)-insulin pentamethyl ester, protected with Boc- at the two N-terminal amino groups, was prepared as described in the preceding XVth communication[6]. The free carboxyl group of the glutamic acid residue B21 of this compound was coupled to the following synthetic oligopeptide esters (X = Lys or Ala): X-Gly-OMe X-Gly-Phe-OMe X-Gly-Phe-Phe-OME X-Gly-Phe-Phe-Tyr-OMe X-Gly-Phe-Phe-Tyr-Ala-OMe After coupling, the semisynthetic products were deprotected and purified. Their biological activities were determined in the mouse fall test and by measurement of blood glucose levels. There were no statistical differences between the values obtained for the lysine B22 and alanine B22 products. The three-step increase in activity due to the amino acids Phe-Phe-Tyr (B24--26) was still recognizable, but compared with the analogues containing arginine B22, the activities were very stronly diminished. These results are in contrast with the assumption that activity of insulin is dependent on the formation of a strong ionic linkage between the asparagine-A21 carboxyl group and any positive charge in B22. The results, however, demonstrate the high specificity of the arginine guanidino group in position B22.