The presence of essential arginine residues at the active sites of citrate lyase complex from Klebsiella aerogenes

The acyl-transferase and acyl-lyase activities of $\text{Klebsiella aerogenes}$ citrate lyase complex are inactivated by the arginine specific reagents phenylglyoxal and 2,3-butanedione, the former reagent being the more potent inhibitor. Citrate and (3$\text{S}$)-citryl-CoA protect the transferase activity, while acetyl-CoA markedly enhances the rate of the inactivation. (3$\text{S}$)-Citryl-CoA protects the lyase subunit in the complex from inactivation. The kinetics of inactivation suggest the involvement of a single arginine residue at each of the active sites of the transferase and of the lyase subunits.     

Three-dimensional structure of the complex of the Rhizopus chinensis carboxyl proteinase and pepstatin at 2.5-A resolution

An X-ray diffraction analysis has been carried out at 2.5-A resolution of the three-dimensional structure of the Rhizopus chinensis carboxyl proteinase complexed with pepstatin. The resulting model of the complex supports the hypothesis [Marciniszyn, J., Hartsuck, J.A., & Tang, J. (1976) J. Biol. Chem. 251, 7088-7094] that statine (3-hydroxy-4-amino-6-methylheptanoic acid) approaches an analogue of the transition state for catalysis. The way in which pepstatin binds to the enzyme can be extended to provide a model of substrate binding and a model of the transition-state complex. This in turn has led to a proposed mechanism of action based on general acid-base catalysis with no covalent intermediates. These predictions are in general agreement with kinetic studies using several carboxyl proteinases, which together with their sequence homology and their common three-dimensional structures suggest that this mechanism can be extrapolated to all carboxyl proteinases.     

Panchanania andPhragmospathula,two new genera of the Hyphomycetes

Two new Hyphomycetes collected from Jaipur, Rajasthan, India are described.Panchanania jaipurensis gen. et sp.n., collected on dead and dying twigs ofGrewia salvifolia has characteristic solitary stalked blastospores, each with a dark-coloured head and paler stalk, on sympodulae borne on synnemata.Phragmospathula phoenicis gen. et sp.n., collected on dead leaf rachis ofPhoenix sp. has characteristic solitary spathulate phragmospores (blastospores) which are dark-coloured in the middle and paler at the ends and are produced on short conidiophores capable of proliferation from within. On the basis of the mode of development of the spores, both fungi are placed in the Torulaceae Corda emend. Subram.     

Toxic and antigrowth effects of raw and processed field bean (Dolichos lablab) on albino rats

Samples of freeze dried green field bean (Dolichos lablab) and dry mature bean, were subjected to the following processing methods—heat processing, extraction with 80% ethanol, hexane or dilute acid, protein isolation; and these samples were evaluated for growth promoting value and toxicity. Extraction with 80% ethanol or with dilute acid increased survival period of the animals; but these did not promote growth. Heat processing was essential to destroy antinutritional factors and promote growth. Extraction of the beans with 80% ethanol did not however alter the trypsin inhibitor or haemagglutinin activities. The protein isolate and acid-extracted residue which had low trypsin inhibitor and haemagglutinin activities, did not also promote growth. Thus the trypsin inhibtor and haemagglutinin activities did not completely account for the toxicity to albino rats. However, heat processing of ethanol extracted bean flour indicated that the beneficial effect of ethanol extraction was not apparent, once the samples were heat processed. Dry mature bean dhal was more toxic than the whole bean either dry or green. Supplementation of heat processed field bean with methionine and tryptophan promoted good growth of albino rats and significantly increased the protein efficiency ratio. Part of the Ph.D. thesis entitled “Studies on the factors affecting the nutritive value of field beanDolichos lablab”, University of Mysore, 1977.     

INTRACRANIAL CONVERSION OF LINOLEIC ACID TO ARACHIDONIC ACID: EVIDENCE FOR LACK OF Δ8 DESATURASE IN THE BRAIN

Eleven-day old rats were given intracranial injection of [1-¹⁴C]linoleic acid (all cis 9,12 octadecadienoic acid) and sacrificed after 8 h. Analysis of brain fatty acids showed that 16:0, 18:2, 20:2,20:3 and 20:4 were labeled. Separation by AgN03:Si02 TLC plates followed by reductive ozonolysis characterized thc polyunsaturated fatty acids as 18:2 (Δ9,12), 20:2 (Δ11,14), 20:3 (Δ8,11,14) and 20:4 (Δ5,8,11,14). A smaller amount of 18:3 (Δ6,9,12) was also identified. This initially suggested 20:2 (A1 1,14) as an intermediate in the optional pathway of biosynthesis of arachidonate. However, when [l-14C]eicosadienoic acid (Δ1 1,141 itself was injected in the brain it was converted to 20:3 (Δ5,11,14) (a non-methylene interrupted double bond system) rather than the expected 20:3 (Δ8,11,14). Only a small amount of arachidonate was formed from 20:2 (Δ11,14). Thus it was concluded that 20:2 (Δ11,14) was not an intermediate in the pathways of arachidonate biosynthesis due to lack of Δ⁵ desaturase in thc brain which agrees with the findings of SPKECRER & LEE (1975) in rat liver.     

Helifoline,a pyrrolizidine alkaloid from Heliotropium ovalifolium

The alkaloidal fraction of Heliotropium ovalifolium yielded retronecine and the new pyrrolizidine alkaloid helifoline. Helifoline was formulated as 1α-angelyloxymethyl-8α-pyrrolizidine-2β,7β-diol on the basis of spectroscopic measurements and hydrolysis to the necine base which appears to be identical with croalbinecine.     

The major ribosome binding site of Escherichia coli ribosomal protein S1 is located in its N-terminal segment

We have cleaved protein S1, which is the largest and the most elongated protein of the Escherichia coli ribosome, using cyanogen bromide and isolated two fragments that retain the functional domains of the intact molecule. The fragments (denoted S1-F2a and S1-F2b) showed molecular weights of 24,000 and 22,500 by dodecyl sulphate/polyacrylamide gel electrophoresis. Fragment F2a is shown to be the N-terminal segment containing about 32% of the peptide chain length of S1. Fragment F2b is derived from another (probably C-terminal) region of S1.Fragment F2a binds to 30 S ribosomal subunits with a strength and specificity comparable to the binding of intact S1. It also binds to matrix-bound poly(U) but the binding is salt-sensitive, unlike the binding of intact S1. Fragment F2b binds only very weakly to poly(U) and does not bind to 30 S subunits. These results are discussed with respect to the ribosome binding domain(s) of protein S1 and the possible interdependence of the multiple functional domains in this large protein.