Age‐dependence and free fatty acid modulation of binding kinetics at the benzodiazepine binding site of serum albumin in neonates and adults determined using fast reaction methods.

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Abstract
Binding kinetics at the benzodiazepine binding site of albumin have been determined as a function of age and fatty acid concentration in serum from 32 neonates (umbilical cord blood), 28 adults aged 23-65 years and 24 adults aged 66-101 years using fluorescence-time curves obtained in a Durrum-Gibson stopped-flow apparatus and the specific marker ligand dansylsarcosine. The binding reaction can be described by a 2-step mechanism characterised by four constants: the association rate constant k2 and dissociation rate constant k-2 for the rate limiting step-2; the affinity constant KA' for the formation of an unstable intermediate complex in step-1; the affinity constant KA for the overall reaction. There were marked differences in k2 between the three groups of subjects with highest values occurring in neonates (mean: 296 s-1), intermediate values in adults aged 23-65 years (mean: 200 s-1, P less than 0.001) and lowest values in adults aged 66-101 years (mean: 144 s-1, P less than 0.001). The dissociation rate constants (k-2) averaged 18.5 s-1 overall, showed only minor changes with increasing age and corresponded to dissociation half-lives of 42 ms, 38 ms and 33 ms for neonates, adults 23-65 years and adults 66-101 years respectively. KA' in neonates and in the group of elderly subjects were lower than in adults aged 23-65 years.(ABSTRACT TRUNCATED AT 250 WORDS)