Deamination and reductive deamination of (2-amino-5, 6-dimethylbenzimidazolyl)cobamide. Preparation of (2-hydroxy-5, 6-dimethylbenzimidazolyl)cobamide and (5, 6-dimethyl-[2(-14)C]-benzimidazolyl)cobamide

(2-Amino-5, 6-dimethylbenzimidazolyl)-cobamide (III) is transformed to (2-hydroxy-5, 6-dimethylbenzimidazolyl) cobamide (IV) by nitrous acid. Exchange of the NH2-group by hydrogen with nitrous acid/hypophosphorous acid yields vitamin B12 (I). This reaction completes a cycle vitamin B12 (I)----[carboxy(2-cyanoamino-4,5-dimethylphenyl)amino]cobamide+ ++ (II)----(2-amino-5,6-dimethylbenzimidazolyl)cobamide (III)----vitamin B12 (I), which allows chemical 14C-labelling of vitamin B12. In this procedure cyanogen bromide, which is necessary for the first step, was labelled with [14C] cyanide. By the following reactions a vitamin B12 was formed in which C-2 of the 5, 6-dimethylbenzimidazole moiety is labelled.     

Proprioceptor distribution and control of a muscle reflex in the tibia of spider legs

In spiders, retrograde cobalt staining was used to clarify the distribution and detailed innervation of the three types of proprioceptors in the tibio-metatarsal leg joint: internal joint receptors, lyriform slit sense organs, and cuticular spines and hairs. The axons of all these receptors run in just two lateral, ascending nerves, which had previously been associated only with the internal receptors. Each nerve contains several hundred axons ranging in diameter from 0.1 micron to ca. 10 micron. Each slit of the four tibial lyriform organs is innervated by two bipolar sensory neurons. The lateral nerves are entirely sensory and run just beneath the cuticle, a convenient site for electrophysiological recording. We demonstrate simultaneous nerve and muscle recordings from intact spiders; these, in combination with selective sensory ablations, show that a resistance reflex in the flexor metatarsi muscles is elicited by internal joint-receptor units.     

Spatiotemporal receptive fields: a dynamical model derived from cortical architectonics

We assume that the mammalian neocortex is built up out of some six layers which differ in their morphology and their external connections. Intrinsic connectivity is largely excitatory, leading to a considerable amount of positive feedback. The majority of cortical neurons can be divided into two main classes: the pyramidal cells, which are said to be excitatory, and local cells (most notably the non-spiny stellate cells), which are said to be inhibitory. The form of the dendritic and axonal arborizations of both groups is discussed in detail. This results in a simplified model of the cortex as a stack of six layers with mutual connections determined by the principles of fibre anatomy. This stack can be treated as a multi-input-multi-output system by means of the linear systems theory of homogeneous layers. The detailed equations for the simulation are derived in the Appendix. The results of the simulations show that the temporal and spatial behaviour of an excitation distribution cannot be treated separately. Further, they indicate specific processing in the different layers and some independence from details of wiring. Finally, the simulation results are applied to the theory of visual receptive fields. This yields some insight into the mechanisms possibly underlying hypercomplexity, putative nonlinearities, lateral inhibition, oscillating cell responses, and velocity-dependent tuning curves.     

Pyruvate decarboxylase--potentially inactive in the absence of the substrate

Using two independent methods, it was shown that pyruvate decarboxylase of brewer's yeast/EC 4.1.1.1./showing a sigmoidal v/S-shape and a corresponding activation phase in the product formation is potentially inactive in the absence of its substrate-pyruvate.     

Isolation of Y-chromosomal repetitive DNA sequences of Drosophila hydei via enrichment of chromosome-specific sequences by heterogeneous hybridization between female and male DNA

Male or female DNA of Drosophila hydei was sheared by sonication, denatured, reannealed to different C0t-values and fractionated by hydroxyapatite. The highly repetitive, moderately repetitive and unique fractions of female DNA were denatured again and coupled via diazotization or cyanogen bromide to macroporous Sephacryl S-500. Enrichment of Y-chromosomal sequences was achieved by cycling each of the different fractions of male DNA under optimized hybridization conditions over a column with a manifold excess of immobilized female DNA of the corresponding complexity. Thereby, Y-chromosomal sequences of D. hydei could be enriched about 100-fold for highly and moderately repetitive DNA and about 10-fold for unique DNA. When a library of male D. hydei DNA was screened with Y-enriched highly repetitive DNA, more than 98% of all hybridizing phages contained inserts of repetitive Y-chromosomal DNA of at least four different sequence families.     

The complete amino-acid sequence of C-phycoerythrin from the cyanobacterium Fremyella diplosiphon

The amino-acid sequences of both subunits of C-phycoerythrin from the cyanobacterium Fremyella diplosiphon have been determined. The alpha-subunit contains 164 amino acid residues, two phycoerythrobilin (PEB) chromophores and has a molecular mass of 18,368 Da (protein: 17,192 Da + 2 PEB, one PEB accounting for 588 Da). The beta-subunit consists of 184 residues, three PEB chromophores and has a molecular mass of 20,931 Da (protein: 19,168 Da and 3 PEB: 1,764 Da). The five PEB chromophores (open chain tetrapyrroles) are covalently bound to six cysteine residues (one of them doubly bound to two cysteine residues). On the alpha-subunit, the first chromophore was found at position 84, homologous to the chromophore binding site of the other biliproteins APC, PC and PEC. The second chromophore, unique for the alpha-subunit of PE, is inserted together with a pentapeptide at position 143 a. On the beta-subunit, a doubly bound chromophore is attached to cysteine residues 50 and 61, similar to the rhodophytan phycoerythrins (B-PE and R-PE). The second and third chromophores were found at positions 84 and 155, homologous to the other biliproteins. A unique peptide insertion of 14 amino acid residues (without chromophore) was found at position 141 a-o in the beta-subunit and probably is located in the three-dimensional model near the additional chromophores of the C-PE alpha- and beta-subunits. Both additional chromophores of the C-PE alpha- and beta-subunit may be located at the periphery of the C-PE-trimer. The amino-acid sequence homology between C-PE alpha- and beta-subunit is 26% and to the alpha- and beta-subunits of C-PC from Mastigocladus laminosus 49% and 48%, respectively.