Studying the influence of brain cathepsin D (EC 3.4.23.5) and high molecular weight (HMW) aspartic endopeptidase (EC 3.4.23.-) on the processing of hypothalamic calmodulin-binding coronaro-constrictory peptide factors from the β-chain of globin it was found that only HMW aspartic endopeptidase generates the fragment 31–40 of the β-chain of bovine hemoglobin (Hb) by cleavage of the Leu30-Leu31 and Phe40-Phe41 bonds. Digestion of the β-chain of globin was performed at 37°C at an enzyme/substrate ratio of 1:80 at pH 3.5 using different times of incubation (from 4 h to 10 h). The resulting peptides were separated by reversed-phase high-performance liquid chromatography (HPLC) and then identified by amino acid analysis and Edman degradation. The differences in specificity and activity of these two brain aspartic proteinases could be explained by their different structural features. Our finding provides evidence for a different biological function of these two enzymes. Data obtained give us reason to suppose that HMW aspartic proteinase probably can participate in the processing of the coronaro-constrictory peptide in vivo by limited proteolysis of Hb or Hb-like protein.
