Diketopiperazine formation and N-terminal degradation in recombinant human growth hormone.

A new degradation process has been identified that occurs in recombinant DNA-derived human growth hormone. Non-enzymatic cyclization of the first two amino acids from the N-terminus and subsequent cleavage results in the formation of a diketopiperazine and a truncated variant of rhGH. The truncated protein was separated using hydrophobic interaction chromatography and identified as desPhe1Pro2-rhGH using N-terminal sequence analysis, tryptic mapping, and mass spectrometry.

A turbidimetric method to determine visual appearance of protein solutions.

An instrumental method to analyze protein solutions for visual appearance is described which is based on spectrophotometric comparison to reference suspensions with varying degrees of turbidity. This method provides a useful substitute for visual inspection of uniform opalescent suspensions in that it is more convenient and less time-consuming and has the potential to be more reproducible, accurate and objective. Established categories of opalescence based on European Pharmacopoeial reference suspensions were determined using turbidity measured as optical density in the 340-360 nm range.

Effect of freezing on aggregation of human growth hormone.

The effect of freezing on formation of soluble and insoluble aggregates of human growth hormone (hGH) was studied. The amount of soluble aggregates was affected very little by freezing regardless of the cooling rate. In contrast, the formation of insoluble aggregates (particulates), as determined by light scattering in the 340- to 360-nm range, was found to increase sharply with increasing cooling rates.

Interaction of human serum apolipoprotein B with sodium deoxycholate.

Preparation of apolipoprotein B (Apo B)-deoxycholate (DOC) complexes by gel filtration chromatography in the presence of 20 mM DOC, pH 8.5, gave two populations of particles with 5% (peak I) and 13% (peak II) lipid remaining bound. These complexes were initially shown to be very large and elongated, with partition radii of approx.

Human serum low density lipoprotein-sodium deoxycholate interaction.

The binding of sodium deoxycholate to low density lipoprotein (LDL) is a relatively fast process, as compared to the lipid displacement reaction and solubilization. The initial reaction has a bimolecular rate constant of approximately 539 M-1 S-1. In the presence of 1 mM sodium deoxycholate, below critical micelle concentration, 0.