Regulation of biosynthesis of aspartate family amino acids in the photosynthetic bacterium Rhodopseudomonas palustris

The four amino acids of the aspartate family (l-lysine, l-methionine, l-threonine, and l-isoleucine) are produced in bacteria by a branched biosynthetic pathway. Regulation of synthesis of early common intermediates and of carbon flow through distal branches of the pathway requires operation of a number of subtle feedback controls, which are integrated so as to ensure balanced synthesis of the several end products. Earlier studies with nonsulfur purple photosynthetic bacteria were instrumental in revealing the existence of alternative regulatory schemes, and in this communication we report on the control pattern of a representative of this physiological group not previously investigated, Rhodopseudomonas palustris. The results obtained from study of the properties of four key regulatory enzymes of the aspartate family pathway (-aspartokinase, homoserine dehydrogenase, homoserine kinase, and threonine deaminase) and of the effects of exogenous amino acids (i. e., the end products) on growth of the bacterium indicate that the control schema in Rps. palustris differs substantially from the schemes described for other Rhodopseudomonas species, but resembles the regulatory pattern observed in Rhodospirillum rubrum.Abbreviations A absorbancy - AK -aspartokinase - ASA aspartate -semialdehyde - DTT dithiothreitol - HS l-homoserine - HSDH homoserine dehydrogenase - HSK homoserine kinase - I l-isoleucine - KU Klett-Summerson photometer units - L l-lysine - M l-isoleucine - KU Klett-Summerson photometer units - L l-lysine - M l-methionine - ME -mercaptoethanol - PABA p-aminobenzoic acid - T l-threonine - TD threonine deaminase - RCV synthetic growth medium (see text) - YP agar medium containing 0.3% yeast extract, 0.3% peptone, and 1.5% agar - Y2T synthetic growth medium (see text)     

A mass-spectrometric sequence study of the enzyme ribitol dehydrogenase from Klebsiella aerogenes

The first detailed results of the application of a low-resolution mixture analysis approach to the sequence analysis of an enzyme, ribitol dehydrogenase, are given. Examples of the interpretation of the spectra of peptide mixtures derived from this protein are described. Evidence for new fragmentation patterns observed is reported, together with an explanation of the generation of ambiguous sequences by use of a low-specificity enzyme, thermolysin. The overall sequencing strategy evolved is assessed.     

Dihydrofolate reductase: low-resolution mass-spectrometric analysis of an elastase digest as a sequencing tool (Short Communication)

An elastase digest of a protein of unknown structure, dihydrofolate reductase, was studied by mass spectrometry. This soluble digest contained a large number of small peptides in different yields, within the ideal molecular-weight range (200-1200) for mixture-analysis mass spectrometry. Sequences of the major component peptides in the digest are reported.     

MEIOSIS IN THE OOMYCETES: I. A MICROSPECTROPHOTOMETRIC ANALYSIS OF NUCLEAR DEOXYRIBONUCLEIC ACID IN SAPROLEGNIA TERRESTRIS

A cytological and cytochemical examination of Saprolegnia terrestris Cookson was undertaken to resolve the conflict of opinion regarding the life cycle of fungi in the Saprolegniaceae, i.e., whether meiosis is zygotic or gametic. Microspectrophotometric analysis reveals that pre-divisional oogonial and antheridial nuclei are 4C; a subsequent reduction division in the sex organs produces 1C male and female gametes. These division products coexist in the developing oospore and presumably fuse to produce the diploid zygote. Analysis of the somatic hyphal nuclei shows a 2C DNA content, with the characteristic skew and bimodal character indicative of predominantly G1, and some S-period and G2 types. The evidence is completely consistent with gametic meiosis, i.e., a predominant diploid vegetative phase and short haploid phase, and refutes the notion of zygotic meiosis. Further ramifications of the work are discussed along with preliminary results of related work in progress.