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The diethylphosphorodithioic acid chelates of Pb(II), Cd(II), Zn(II) and Mn(II) in ethanol and water-ethanol solutions, give irreversible polarographic waves which have been made use of in the calculation of the over-all chelate formation constants. The logarithm of the chelate formation constant was found to be a linear function of the dielectric constant of the ethanol-water medium. In these metal chelates in which the metal-sulphur bonds are ionic, the chelate stability sequence, Pb(II) > Cd(II) > Zn(II) > Mn(II), is the same as that found with other sulphur ligands in which the metal-sulphur bonds have much less ionic character.

(i) Saccharomyces cerevisiae grown in the presence of 1.0 mM l -tryptophan slowly excreted fluorescent material that was chromatographically identifiable as 3-hydroxyanthranilate but did not excrete detectable amounts of anthranilate nor rapidly deplete the medium of l -tryptophan. Under similar growth conditions, Neurospora crassa rapidly excretes anthranilate and rapidly depletes the medium of l -tryptophan. (ii) Chromatographic analysis of crude extracts from yeast revealed a single kynureninase-type enzyme whose synthesis was not measurably affected by the presence of tryptophan in the medium. Previous studies have provided evidence for two kynureninase-type enzymes in N. crassa , an inducible kynureninase and a constitutive hydroxykynureninase. (iii) Kinetic analysis of the partially purified yeast enzyme provided Michaelis constants for l -3-hydroxykynurenine and l -kynurenine of 6.7 × 10 −6 and 5.4 × 10 −4 M, respectively. This and other kinetic properties of the yeast enzyme are comparable to those reported for the constitutive enzyme from N. crassa . (iv) These findings suggest that S. cerevisiae has in common with N. crassa the biosynthetic enzyme hydroxykynureninase but lacks the catabolic enzyme kynureninase. Therefore, it can be predicted that, unlike N. crassa, S. cerevisiae does not carry out the tryptophan-anthranilate cycle. Distinct kynureninase-type enzymes may exist in other microorganisms and in mammals.

The polarographic behaviour of bis -(O,O′-diethyldithiophosphato) nickel (II), Ni(DTP) 2 , at the dropping mercury electrode has been examined in ethanol and ethanol-water media. In ethanol, a single wave that is almost completely controlled by diffusion is obtained and has been attributed to the catalytic reduction of nickel (II) in the presence of the complexing agent, DTP. In ethanol-water mixtures, in which the water content is less than 40% v/v, two waves are obtained. The first wave is the catalytic wave that arises from the complexed nickel (II) and the second wave is the reduction wave of nickel (II) that is not complexed by DTP. In the presence of acid, in addition to the nickel wave, a catalytic hydrogen wave is also obtained. Mechanisms involving adsorption and complexation have been proposed for both catalytic waves. Nickel (II) forms with DTP, relatively weak complexes in which the nickel-sulphur bond is readily disrupted when the dielectric constant of the solvent medium is increased.

Nickel(II) in the presence of xanthate undergoes catalytic reduction at the dropping mercury electrode in ethanol and ethanol-water media at potentials more positive than those at which nickel(II) is reduced in the absence of xanthate. The properties of the catalytic wave have been examined and a mechanism that has been proposed previously for other systems that give catalytic reduction waves has been shown to apply [1]. The limiting current of the catalytic wave can be primarily diffusion controlled[1] or kinetically controlled; examples of both types of mechanisms have been found in studies on the reduction of nickel(II) in the presence of bidentate ligands containing two sulfur donor atoms. In the nickel(II) xanthate system, the presence of catalytic hydrogen waves caused difficulties in the interpretation of the polarographic data.

A comparative analysis of the kynureninase-type activity found in various organisms has demonstrated two forms of enzyme. One, inducible by tryptophan, has a relatively low Km for L-kynurenine, and is found in microorganisms such as Pseudomonas fluorescens and Neurospora crassa. The other, unaffected by tryptophan, has a low Km for L-3-hydroxykynurenine and is found in a wide variety of organisms, including molds, amphibia, birds and mammals. The yeast Saccharomyces cerevisiae lacks the inducible kynureninase but contains the constitutive enzyme termed an hydroxykynureninase. As a result, the yeast, unlike M. crassa, excretes 3-hydroxyanthranilate in response to L-tryptophan. However, initial studies indicate that little if any 3-hydroxyanthranilate accumulates in beer, wine or bread. Although 3-hydroxyanthranilate is suspect as an endogenous carcinogen, its carcinogenicity as an exogenous agent has not been shown.

The kynureninase-type enzymes of three fungi and one bacterium were isolated and examined kinetically for their ability to catalyze the hydrolysis of L-kynurenine and L-3-hydroxykynurenine. The phycomycete Rhizopus stolonifer was found to contain a single, constitutive enzyme with Km for L-3-hydroxykynurenine and L-kynurenine of 6.67 times 10-minus 6 and 2.5 times 10-minus 4 M, respectively. The ascomycetes Aspergillus niger and Penicillium roqueforti each contain an enzyme, induced by L-tryptophan, with similar Km for L-3-hydroxykynurenine and L-kynurenine ranging from 5.9 times 10-minus 5 to 14.3 times 10-minus 5 M, as well as a constitutive enzyme with Km for the two substrates of similar to 4 times 10-minus 6 M and 10-minus 4 M. The bacterium Pseudomonas fluorescens has a single, inducible enzyme with Km for L-3-hydroxykynurenine and L-kynurenine of 5 times 10-minus 4 and 7 times 10-minus 5 M. In addition, significant differences in maximal velocities (Vmax) were observed in two cases. The Vmax of the inducible activity from P. fluorescens was 4.5 times greater for L-kynurenine than L-3-hydroxykynurenine, whereas the Vmax of the constitutive activity from R. stolonifer was 2.5 times greater for L-3-hydroxykynurenine. It is concluded (i) that the constitutive activities are hydroxykynureninases involved in the biosynthesis of nicotinamide adenine dinucleotide from L-tryptophan, (ii) that the inducible activities are kynureninases involved in the catabolism of L-tryptophan to anthranilate, and (iii) that R. stolonifer and P. fluorescens, respectively, carry the most specific examples of each type of enzyme.

1. delta-Aminolaevulate dehydratase (EC 4.2.1.24) was purified 80-fold from tobacco leaves and its properties were studied. 2. The enzyme had optimum pH7.4 in potassium phosphate buffer, K(m)6.25x10(-4)m at 37 degrees and pH7.4, optimum temperature 45 degrees and an activation energy of 11100 cal./mole. 3. The enzyme lost activity when prepared in the absence of cysteine, and this activity was only partly restored by the later addition of thiols. Reagents for thiol groups inactivated the enzyme. 4. Mg(2+) was essential for activity, and EDTA and Fe(2+) were inhibitory; Mn(2+) was an activator or an inhibitor depending on the concentration.

Experiments were conducted on Nicotiana tabacum , L. to study the relation in the grana among chlorophylls, carotenoids, and proteins. The effect of iron chlorosis on protein and pigment synthesis was studied at different stages of chlorosis using glycine-U-C 14 . Pigments were separated by thin layer chromatography. Chlorophyll a, chlorophyll b, carotenoid, and protein contents of chloroplasts from chlorotic tissue were less than those of normal tissues. A 25% decrease in protein labeling and a 45% decrease in chlorophyll labeling was noted in deficient tissue compared to normal tissue even before chlorosis was perceptible. Both normal and iron deficient leaf discs which received iron in the incubation medium incorporated higher amounts of radioactive glycine into chlorophyll a and chlorophyll b at all stages of development than their respective counterparts not supplied with iron in the incubation medium. The presence of iron in the incubation medium reduced the amount of glycine incorporated into carotenes and xanthophylls, except where the tissue was severely chlorotic. This may be attributed to active competition for glycine between the iron-dependent- (chlorophyll) and iron-independent-(carotenoid) biosynthetic pathways. Incorporation of glycine into chloroplast pigments was lowest at severe chlorosis, probably due to a reduction in the overall enzyme activity.

The structure of the five-co-ordinate intermediate formed by the displacement of a co-ordinated sulphur atom in the four-co-ordinate chelate, bis-(O,O′-dimethyldithiophosphato)nickel(II) by the ligand 2,9-dimethyl-1,10-phenanthroline, has been determined.