Molecular mass determination for prostate-specific antigen and alpha 1-antichymotrypsin complexed in vitro

The results from molecular mass determinations and amino acid analyses for prostate-specific antigen (PSA), alpha 1-antichymotrypsin (ACT) and PSA-ACT complexed in vitro are reported. Molecular masses for two separate PSA-ACT lots were determined by matrix-assisted laser desorption ionization mass spectroscopy (MALDI-MS) coupled to a time-of-flight (TOF) detector. Interestingly, both PSA-ACT lots contained two predominant protein species: 78,095 +/- 138 Da (approx. 67% of total protein) and 82,519 +/- 104 Da. Because a heterogneous population was observed and the masses were less than expected on the basis of less sensitive techniques, molecular masses for the individual PSA and ACT components were determined. As expected, PSA possessed a single molecular mass (27,755.8 Da). Each ACT raw material lot, however, also contained two predominant species: 55,106 +/- 111 and 51,414 +/- 32 Da. To assess the amino acid composition, each PSA, ACT and PSA-ACT lot was subjected to acid hydrolysis for 24, 48 and 72 h followed by amino acid analysis. Experimental results, expressed as mole percentages for each measurable residue and the number of residues per mole of protein, were compared with both the predicted and previously published values and were as expected. These more accurate molecular mass values for ACT and purified PSA-ACT complex should be considered in preparing and characterizing international standard preparations.