Latch model

In intact smooth muscle, phosphorylation often declines while force is maintained, the so-called "latch" state (Dillon etal., 1981). Regulation of the latch state is still poorly understood. It has been very difficult to induce a latch state in skinned smooth muscle. The closest may be triton skinned chicken gizzard, which contracts independent of MLC phosphorylation (Wagner and Ruegg, 1986). In skinned chicken gizzard, but also in other types of smooth muscle (Bialojan et al., 1987 Siegman et al., 1989 Kenney et al., 1990 Schmidt et al, 1995), a steep and nonlinear relation between force and MLC phosphorylation was observed, which was postulated by the "latch model" of Hai and Mur-... 

A high phosphatase rate was taken as the basis of a new form of the latch model by Driska (1987) and Hai and Murphy (1988). In this model, LC20 phosphorylation is considered to be the only switch for crossbridge turnover, and the nonlinear relation between force (Jatp) and maximal shortening velocity (Vj ax) arises because of a significant rate of LC20 dephos-... 

The Hinge and Latch Model of Keapl-Nrf2 Interaction. 247... 

Fig. 5 Overview of the current hinge and latch model of Nrf2 regulation, (a) In the absence of cellular stress, the Keapi homodimer binds both the DLG and motifs of a single...

Tong KI, Kobayashi A, Katsuoka F, Yamamoto M. 2006. Two-site substrate recognition model for the Keapl-Nrf2 system a hinge and latch mechanism. Biol Chem 387 1311-1320. 

Based on this design a memory/adder model (Fig. 6(c)) using 464 transistors could be constructed and evaluated on grounds of SPICE circuit simulations. Four bits of information were read from four different memory cells, added as two 2-bit words, and the resulting 2-bit was moved through registers (clocked D-latches) to a subsequent computation. It must be noted... 

Arithmetic operations as conditional expressions, as in the previous example, should be avoided when inferring latches since there is a very high probability of race condition between the conditionals in the synthesized netlist this might cause the latched value in the synthesized netlist to differ from that in the Verilog HDL model. 

In the previous example, the output is also saved in a flip-flop. What if a non-latched output is required In this case, the assignments to Z can be separated out into a second always statement, as shown in the model next. 

Synthesis infers four flip-flops for this model, three for variable Previous and one for SeqFound. However, optimization reveals that one of the flip-flops for Previous is not necessary and hence it is removed. In this model, the output is latched since it is assigned a value under the control of a clock edge. If a latched output is not desired, then the assignment to SeqFound must be done outside the always statement. Such a module is shown next. 

Because of these problems, different synthesis systems support different Verilog HDL subsets for synthesis. Since there is no single object in Verilog HDL that means a latch or a flip-flop, each synthesis system may provide different mechanisms to model a flip-flop or a latch. Each synthesis system therefore defines its own subset of Verilog HDL including its own modeling style. 

A model involving cooperativity has been proposed as an alternative to the Hai and Murphy formulation (Vyas et al., 1992, 1994). The models are similar in that in both models cross-bridges exist in the same four basic states. The novelty of this model is a finite attachment rate of unphosphorylated cross-bridges (kg in Fig. 2B), which is dependent on the number of attached, phosphorylated cross-bridges (AMp). In effect, some slowly cycling "latch-bridges" are postulated to form cooperatively as a result of the attach-... 

---