Mutants affected in lamB, the structural gene for phage lambda receptor, are unable to utilize maltose when it is present at low concentrations (less than or equal 10 muM). During growth in a chemostat at limiting maltose concentrations, the lamB mutants tested were selected against in the presence of the wild-type strain. Transport studies demonstrate that most lamB mutants have deficient maltose transport capacities at low maltose concentrations. When antibodies against purified phage lambda receptor are added to a wild-type strain, transport of maltose at low concentrations is significantly reduced. These results strongly suggest that the phage lambda receptor molecule is involved in maltose transport.

The kinetic parameters for the maltose transport system in Eschevichiu coli K12 were determined with maltose and maltotriose as substrates. The system exhibits an apparent K, of 1 pM for maltose and 2 pM for maltotriose. The V of entry was determined as 2.0 and 1.1 nmol substrate/min per lo8 cells. Mutations in IamB, the structural gene for the receptor protein of phage 1, increased the K, for maltose transport by a factor of 100-500 without influencing the maximal rate of transport. Maltotriose is no longer transported in these lamB mutants. The maltose-binding protein, an essential component of the maltose transport system, was found to exhibit substrate-dependent fluorescence quenching. This phenomenon was used to determine dissociation constants and to estimate the rate of ligand dissociation. A K d of 1 pM for maltose and of 0.16 pM for maltotriose was found. From the comparison of the kinetic parameters of transport of maltose and maltotriose in wild-type and ),-resistant mutants with the binding constants for both sugars to purified maltose-binding protein, we conclude that the /z receptor facilitates the diffusion of maltose and maltodextrins through the outer membrane.Wiesmeyer and Cohn first demonstrated a transport system which was energy-dependent and inducible by maltose [I]. Genetic studies performed later on the maltose system revealed that three genes malE, mulF, malK, located in the malB region, are essential in the maltose transport capacity [2] and are under the positive control of a malT gene. It is clear that this transport system is the only one in Eschrvichia coli taking up maltose, since malE, malF or mulK mutants do not grow on maltose.Recently a maltose-binding protein was extracted by osmotic shock, purified to homogeneity, and shown to be an essential element in maltose transport [3], as well as in maltose chemotaxis [4]. The synthesis of this protein is induced by maltose and is under the same positive control as the other proteins of the maltose system. It is coded for by the malE gene. The maltose-binding protein is a monomer of 40000 molecular weight and it recognizes maltose and the a,l+4-linked higher maltodextrins. Gene IumB, located in the same operon as malK, is the structural gene for an outer membrane protein which acts as a receptor for bacteriophage 1 [ 5 ] . IamB mutants have recently been shown to be impaired in maltose transport when the concentration of this sugar in the medium is less than 0.1 mM. Furthermore, treatment of wild-type bacteria (IamB') with antibodies directed against purified 1 receptor strongly reduced the initial rates of maltose transport, thus demonstrating that the phage receptor is an element of the maltose uptake machinery [6]. In the present publication we have determined the kinetic parameters of maltose transport in wild-type and 2-resistant mutants. In addition, we have demonstrated that the maltose-binding protein undergoes a substate-dependent decrease in intrinsic fluorescence. This property has enabled us to rapidly determine binding c...

A “periplasmic” maltose binding protein was purified from Escherichia coli. This protein is shown to be under the same positive control as the whole maltose system, and its synthesis is inducible by maltose. This binding protein is coded by malE, one of the three cistrons of the malB region involved in the transport of maltose. The binding characteristics of this protein, as well as the kinetics of release of bound maltose, suggest that the binding protein can exist in two states differing by their affinity towards maltose. The significance of this result is discussed in view of the role that the protein is believed to play in maltose transport.

When a solution of binding protein and its ligand is dialyzed against a large volume of ligand-free medium, the rate of exit of the ligand from the proteincontaining compartment can be extremely slow, much slower than the rate observed in the absence When a solution of a binding protein and its ligand is dialyzed against a very large volume of buffer, the rate of disappearance of the ligand from the dialysis bag may be much smaller than it would be from a bag containing no protein. One may be inclined to believe that, with such a system, the rate of exit of ligand from the bag is a measure of the rate of dissociation of the protein-ligand complex (1-5). However, this is not the case. Although the real significance of the retention of ligand by protein is undoubtedly obvious to many, it has been so often misunderstood that the present discussion appears justified.The conclusion will not apply only to dialysis, but also to other experimental systems where apparently "out of equilibrium" situations are observed. The retention effect may also have some significance in certain phenomena, such as bacterial chemotaxis.

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