Study of the nature of beta-lactamase activity of blood serum
Zhyltsou I.V., Veremey I.S., Semenov V.M., Generalov I.I., Egorov S.K.
In the presented study we have shown that beta-lactamase activity is intrinsic property of human blood serum. This activity is medicated by human serum albumin (HSA) fraction by 86-100%. Purified HSA preparations of different origin with concentration corresponding to the normal serum one possess their proper beta-lactamase activity compatible with one of native blood serum. Besides HSA, the majority of protein blood fractions possess low level beta-lactamase activity what composes about 9,6% of the whole serum activity. Polyclonal IgG of 1, 2 and 4 subclasses also possess some beta-lactamase activity but their contribution to the total serum beta-lactamase activity doesn’t exceed 10-15%. Activity of 1 M of HSA 3,8-fold exceeds that of 1 M polyclonal IgG. Optimal pH for HSA beta-lactamase activity is about 9,0. Meanwhile, extraordinary high growth of activity level takes place in increase of pH from 7,0 to 8,0. Beta-lactamase activity of human blood increases substantially with the rise of body temperature, and in patients with high fever it may be significantly (by 44,6%) higher than in persons with normal body temperature. Increase of ionic strength of solution leads to decline in beta-lactamase activity of HSA. Kinetics of nitrocefin decay under the influence of HSA corresponds to the 1st degree reaction with Km=0,115. Intact tertiary structure of HSA is crucial for manifestation of its beta-lactamase activity what suggests presence of active site in albumin molecule resembling that of true bacterial beta-lactamases; nonetheless, this activity obviously doesn’t depend upon the presence of cofactors.