Swinging door mechanism

Henderson and Johnston [59] based on their work with alanine racemase from B. subtilis proposed catalysis by a single base with motion of the coenzyme-substrate complex in a process they termed a swinging door mechanism (Scheme IX). Their proposed mechanism is based on the observation of pronounced asymmetry in the interaction of many racemases with their enantiomeric substrates [55], for example, in the inactivation of the enzyme by D- and L-/I-chloroalanine [59]. The position of the door relative to the point of protonation/deprotonation would determine whether a D- or an L-amino acid is interacting with the enzyme, and if one position were more stable than the other, the enzyme would interact differently with a D- and an L-isomer. 

Scheme IX. Swinging door mechanism for PLP-dependent enzymatic amino acid racemization (from [57]).

A safety door mechanism to prevent opening while the unit is under pressure. The locking device may be actuated directly by internal pressure or indirectly through an automatic switch. The door itself may be the swing-out or sliding type. 

Fig. 8.8 Swinging-door model for mechanism of alanine racemase reaction. (Reproduced with permission from Henderson and Johnston, Biochem. Biophys. Res. Commun., 68, 797 (1976)).

Some lifts use electrohydraulic actuators to hft and fold, with valves and gravity used to lower the lift. Crane lifts may swing out from a post at the front or rear of the side door. Interlocking mechanisms are available with some lifts to prevent the lift from being operated while the door is closed. The Society of Automotive Engineers (SAE) has developed guidelines for the testing of wheelchair lift devices for entry and exit from a personal vehicle. The standards are intended to set an acceptable level of reliability and performance for van hfts. 

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