Summary
cDNAs for protein C inhibitor (PCI) were cloned from human and rhesus monkey[
1
] liver RNAs by reverse transcription and polymerase chain reaction (PCR) amplification.
Sequencing showed that rhesus monkey and human PCI cDNAs were 93% identical. Predicted
amino acid sequences differed at 26 of 387 residues. Pour of these differences (T352M,
N359S, R362K, L3631) were in the reactive center loop that is important for inhibitory
specificity, and two were in the N-terminal helix (M8T, E13K) that is implicated in
glycosaminoglycan binding. PCI in human or rhesus monkey plasma showed comparable
inhibitory activity towards human activated protein C in the presence of 10 U/ml heparin.
However, maximal acceleration of the inhibition of activated protein C required 5-fold
lower heparin concentration for rhesus monkey than for human plasma, consistent with
the interpretation that the additional positive charge (E13K) in a putative-heparin
binding region increased the affinity for heparin.