Effect of immobilization on the penicillin binding and reactivity properties of DD-peptidase from Streptomyces R61

An affinity gel matrix containing an enzyme (DD-peptidase) with specific beta-lactam binding properties was characterized with respect to its binding and reactivity behavior with penicillin. The data show that immobilization of DDP by reaction with the enzymes susceptible amino groups resulted in changes in catalytic activity on a tripeptide substrate, penicillin binding efficiency and pH stability of drug binding. Properties unaffected by immobilization were the drug-enzyme complex stability, binding reaction mechanism, drug selectivity and method of complex desorption. The affinity of DDP for penicillin-G was investigated by surface plasmon resonance. These characteristics were compared with those of the soluble enzyme. Conditions for elution of the bound drug were determined and a method for immobilizing Streptomyces DDP by which its binding site structure is sustained was also evaluated.

Structural changes associated with the spontaneous inactivation of the serine proteinase human tryptase

Human skin tryptase, a serine proteinase stored within mast cell secretory granules, rapidly loses enzymatic activity in solutions of physiological salt concentration, pH, and temperature. The inactivation of tryptase can be slowed and even reversed by addition of heparin, a highly sulfated glycosaminoglycan also found in the secretory granules. These properties may be relevant to tryptase regulation after secretion from mast cells. To further characterize the molecular changes underlying the functional instability of tryptase, circular dichroism (CD) and analytical ultracentrifugation were used to investigate structural changes during spontaneous inactivation. The CD spectra of active and spontaneously inactivated tryptase are different, particularly in the region around 230 nm where active tryptase displays a distinct negative peak. This peak is also observed in the CD spectrum of bovine chymotrypsin but not in trypsin, elastase, or chymotrypsinogen. Loss of activity resulting from spontaneous inactivation was accompanied by a diminution of the 230-nm signal. The kinetics for the signal loss appeared to be first-order and closely paralleled the rate of enzymatic activity loss. Dextran sulfate, a highly sulfated polysaccharide, was capable of reactivating tryptase and restoring the CD signal. After 2 h of decay (> 90% loss of activity), addition of dextran sulfate resulted in an almost immediate return of the CD signal to that of active tryptase. The return of the CD signal appeared to be more rapid than the return of enzymatic activity, thereby suggesting the presence of an unidentified step which is rate-limiting for activity return (and loss) and subsequent (prior) to the CD change accompanying activity loss. Ultracentrifugation analysis of tryptase showed a marked change in its association state upon inactivation. Sedimentation equilibrium under stabilizing conditions demonstrated the presence of a single species with the molecular weight of a tetramer. After spontaneous inactivation, a mixture of species was evident, which was characterized as monomers and tetramers in equilibrium. These results demonstrate that spontaneous inactivation of tryptase is associated with reversible conformational changes and that a consequence of inactivation is the formation of a destabilized tetrameric form. Although the molecular mechanism initiating these changes remains unclear, possible insights into the process are discussed on the basis of the similarity between the CD spectra of tryptase and chymotrypsin.

Human skin tryptase: kinetic characterization of its spontaneous inactivation

The spontaneous loss of human tryptase hydrolytic activity was investigated. Time course studies monitoring the loss in catalytic activity were biphasic and correlated with a reduction in the concentration of catalytic sites. There was an initial rapid phase leading to greater than 85% loss in activity. The remaining activity gradually decayed toward completion over a 40-h period. The initial phase could be described as a first-order process with a t1/2 of approximately 6.0 min in 0.2 M NaCl (pH 6.8, 30 degrees C). The rate constant for this phase showed little, if any, sensitivity to changes in enzyme concentration, consistent with a first-order process, and analysis of the reaction as a function of temperature was consistent with a single rate-determining step. The rate of this process, however, showed marked sensitivity to changes in NaCl concentration and pH. Increasing the NaCl concentration as well as decreasing the pH below the pI (pH 6.3) reduced the rate of activity loss, whereas increasing the pH above pH 8.0 markedly increased the rate of activity loss. The effect of NaCl concentration and pH on the rate of activity loss suggests that the rate-limiting step governing the fast phase of the reaction involves electrostatic interactions. The presence of a fast and a slow phase in the decay process may suggest heterogeneity in the sample or the rapid formation of an inactive, but reversible, intermediate. A reversible intermediate was demonstrated when "inactivated tryptase" was incubated in the presence of heparin, and an increase in tryptase catalytic activity was observed.(ABSTRACT TRUNCATED AT 250 WORDS)