A method to determine the kinetics of multiple proteins in human infants with respiratory distress syndrome

Abstract

We report a method to measure in vivo turnover of four proteins from sequential tracheal aspirates obtained from human newborn infants with respiratory distress syndrome using targeted proteomics. We detected enrichment for all targeted proteins approximately 3 h from the start of infusion of [5,5,5-(2)H(3)] leucine, secretion times that varied from 1.2 to 2.5 h, and half lives that ranged between 10 and 21 h. Complement factor B, a component of the alternative pathway of complement activation, had an approximately twofold-longer half-life than the other three proteins. In addition, the kinetics of mature and carboxy-terminal tryptic peptides from the same protein (surfactant protein B) were not statistically different (p = 0.49).

Figures

Figure 1

Enrichment curves (Tracer-to-tracee ratio vs. time) corresponding to A) SP-B (C-terminus peptide); B) prosaposin; C) complement factor B; and D) lactotransferrin. Enrichment was readily observed 3 hours from the start of infusion. Significantly higher levels of enrichment were observed for SP-B and lactotransferrin. Infusion of [5,5,5-2H3] leucine ended after 6 hours.

Figure 2

A) The protein sequence of Pro-SP-B displaying the N-terminus (blue), mature (black) and C-terminus (red) forms of the protein. The underlined peptides were targeted for analysis. B) A comparison between the enrichment curves of peptides from the C-terminus (i.e., nonfunctional form) and from the mature (i.e., functional form) form of SP-B. Both peptides demonstrate similar kinetics. The difference in the average calculated half life between the two peptides was insignificant (p=0.49).