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This paper deals solely with idiotypic determinants, the configurations of which are modified when the antibody bearing them interacts with its ligand. This phenomenon is measured as an inhibition of the reaction between anti-idiotype and idiotype. Two points are made: (a) The assay for ligand-modifiable determinants can be used to determine the "size" of the combining site. This is illustrated here with the anti-α(1 → 6) dextran mouse myeloma immunoglobulin W3129. Whether the interaction between a homologous series of α(1 → 6) oligosaccharide ligands and the combining site of W3129 is measured by inhibition of precipitation with α(1 → 6) dextran (4) or of binding of W3129 to anti-W3129 idiotype, the finding is the same. The order of inhibition is isomaltohexaose = isomaltopentaose >> isomaltotetraose > isomaltotriose >>> isomaltose. The combining site is optimally complementary to isomaltopentaose. (b) Cross-idiotypic specificity is closely correlated with cross-combining specificity; the converse is not true. This is illustrated here with three groups of mouse myeloma immunoglobulin, each specific for α(1 → 3) dextran, α(1 →6) dextran, ß(2 → 1) or ß(2 → 6) levan. If a given anti-idiotypic serum cross-reacted with several myeloma proteins, they always had similar combining specificity. Thus the three proteins, J558, MOPC 104E, and UPC 102, which cross-react with anti-J558 have combining specificity for α(1 → 3) dextran; cross-reacting W3082, UPC 61, and Y5476 have specificity for levan; and cross-reacting W3129 and W3434 have specificity for α(1 → 6) dextran. This extends previous studies with proteins specific for phosphorylcholine (7) or γ-globulin (8). As expected, the converse is not true, for proteins may have combining specificity for α(1 → 6) dextran e.g. QUPC 52, or levan e.g. J606, UPC 10 and yet not carry the above-mentioned reference idiotypes. The correlation between cross-idiotypic and combining specificity breaks down when idiotypic determinants which are not modifiable by ligand are studied. The implications of this are pointed out since most investigations deal with ligand-nonmodifiable determinants.

Cooperativity of ligand binding is defined operationally in terms of the Hill parameter n , whose values uniquely define the shape of the binding curve. When n is everywhere equal to 1 the system behaves as if the sites were all the same and independent. If at any point n is unequal to 1 the system is either cooperative ( n > 1) or anticooperative ( n < 1) at that point. This means that the binding of ligand at any site is influenced by the presence or absence of ligand at other sites. In the present paper this influence is formulated in terms of probabilities of the various binding events and of conditional probabilities which relate them. The result is a network of linked probabilities which determine the cooperativity or anticooperativity of the system. This probabilistic formulation supplements the more usual one in terms of free energies and places the subject in a broader perspective.

The paper describes the isolation and properties of several rhenium complexes viz., [ReCl3 (dipy)(NO)], (ReCl3 (phen)(NO)], [ReCl(dipyMNO)](ClO4)2and [ReCl(phen)2(NO)](ClO4)2where dipy and phen stand for 2,2'-dipyridyl and 1,10-phenanthroline respectively. The non-electrolytes are insoluble in water and in common organic solvents but are soluble in concentrated sulphuric acid from which they can be reprecipitated unchanged. The cationic compounds are soluble in water, acetone and ethanol. All these a.re weakly paramagnetic at room temperature. The infra-red spectra of the non electrolytes show sharp bands at 1740 cm-1 (dipyridyl compound) and 1760 cm-1 (phenanthroline compound).

This paper analyzes, in terms of a triangular kinetic scheme, the possible effects of an intermediate in the photochemical behavior of simple heme proteins. Both steady-state and transient phenomena are analyzed. The magnitude of the quantum yield for a given system is determined by a competition between quenching and ligand detachment, measured by the two rate constants, κ -1 and κ 2 , respectively; as a first approximation, it can be described by a single parameter, namely the ratio κ -1 /κ 2 . The individual values of κ -1 and κ 2 can only be determined at light intensities so high that the measured quantum yield becomes itself a function of light intensity. Under these conditions the relaxation time for transient approach to the steady-state can be complex, corresponding to heavily damped chemical oscillations. It is pointed out that when the model is extended to include more than one intermediate, multiple oscillations are possible. In this more general case the system in the steady-state may also show pseudocooperativity or anticooperativity.

This paper deals with the study of the cupric complexes of some substituted ortho-hydroxy-azo dyes, viz., 6-hydroxy-azo-benzene-3-methyl-2'-nitro-4'-sulphonic acid (abbreviated to 3-methyl-2'-nitro­-4'-sulpho dye), 2,3-dimethyl-4'-sulpho dye, 2'-chloro-3-methyl-4'-sulpho dye and 3-methyl-4'-sulpho dye.