Ethoxyformylation of histidine residues in equine growth hormone.

The research article investigates how histidine residues in equine growth hormone react to ethoxyformic anhydride. This study reveals that there are two types of histidine residues in equine growth hormone, each with a different reaction speed to ethoxyformic anhydride.

Research Methodology and Findings

• The researchers studied the behavior of histidine residues in equine growth hormone when introduced to ethoxyformic anhydride.
• Their study found two distinct sets of histidine residues based on their reaction kinetics.
• First group includes histidine 169, which reacts slowly, with a reaction rate constant represented as (k = 0.164 min-1).
• The second group, which reacts faster, includes histidines 19 and 21, having a reaction rate constant denoted as (k = 0.892 min-1).

Correlation with Hormone Binding Capacity

• Further, the study found a correlation between the speed of reaction and hormone-binding capacity. Specifically, the faster the ethoxyformylation of the fast-reacting group (histidines 19 and 21), the more significant the decrease in capacity to compete with 125I-labelled hormone for rat liver binding sites.
• This suggests that the fast-reacting group, i.e., histidines 19 and 21, may be involved in the hormone’s ability to bind to specific receptors in the rat liver.

Circular Dichroism Studies

• Through circular dichroism studies, the researchers found no significant conformational changes in the protein even after all the three histidine residues were modified.
• This suggests that the protein maintains its overall shape and structure despite the reaction with ethoxyformic anhydride, which is important for its function.

Agreement with Bovine Growth Hormone

• The results of this study align with previous findings on bovine growth hormone. This provides further evidence to suggest that histidines 19 and/or 21 are involved in the binding of these growth hormones to their respective receptors.
• It also implies that the results could be broadened to other species, which could be of important scientific and therapeutic value.