A Word Path Puzzle

In each of the 25 five-by-five letter arrays below, a word having no repeated letters can be traced out by horizontal or vertical steps. As you discover the word in each array, place its initial letter in a blank five-by-five square whose cells are defined by the positions of the 25 individual arrays in the square pattern below

Word Weights

In his article Lightweights and Heavyweights in the November 1972 issue of Word Ways, Darryl Francis introduced the concept of weight for words. He then went on to form two lists, one of words that were heavy for their size and another of words that were light for their size. I\u27d like to play around with that concept a bit more in this article

Kickshaws

Kickshaws is currently being assembled by a series of guest editors. All contributions should be sent to the editor in Morristown, New Jersey

Kickshaws

A collection of linguistic kickshaws

Kickshaws

A collection of linguistic kickshaws

Homophone Pairs

Variant pronunciations of words are more common than variant spellings. And just as dictionaries try to reflect accepted spellings, so also do they give common pronunciations. They seldom, of course, catch local accents, twangs, intonations or cadences

Put in a Good Word for Me

This is the first of a pair of articles which invites the reader to use his deductive abilities on lists of words. His task is first to find a common property that the 24 words in a list share, and second to insert the word at the head of this list (given in capital letters) into its proper place within the list

Put In Some More Good Words

This is the second of a pair of articles which invites the reader to use his deductive abilities on lists of words; the first article appeared in the August 1979 Word Ways. His task is first to find a common property that the 24 words in a list share, and second to insert the word at the head of this list (given in capital letters) into its proper place within the list

Deprotonation by Dehydration: The Origin of Ammonium Sensing in the AmtB Channel

The AmtB channel passively allows the transport of NH(4) (+) across the membranes of bacteria via a “gas” NH(3) intermediate and is related by homology (sequentially, structurally, and functionally) to many forms of Rh protein (both erythroid and nonerythroid) found in animals and humans. New structural information on this channel has inspired computational studies aimed at clarifying various aspects of NH(4) (+) recruitment and binding in the periplasm, as well as its deprotonation. However, precise mechanisms for these events are still unknown, and, so far, explanations for subsequent NH(3) translocation and reprotonation at the cytoplasmic end of the channel have not been rigorously addressed. We employ molecular dynamics simulations and free energy methods on a full AmtB trimer system in membrane and bathed in electrolyte. Combining the potential of mean force for NH(4) (+)/NH(3) translocation with data from thermodynamic integration calculations allows us to find the apparent pK(a) of NH(4) (+) as a function of the transport axis. Our calculations reveal the specific sites at which its deprotonation (at the periplasmic end) and reprotonation (at the cytoplasmic end) occurs. Contrary to most hypotheses, which ascribe a proton-accepting role to various periplasmic or luminal residues of the channel, our results suggest that the most plausible proton donor/acceptor at either of these sites is water. Free-energetic analysis not only verifies crystallographically determined binding sites for NH(4) (+) and NH(3) along the transport axis, but also reveals a previously undetermined binding site for NH(4) (+) at the cytoplasmic end of the channel. Analysis of dynamics and the free energies of all possible loading states for NH(3) inside the channel also reveal that hydrophobic pressure and the free-energetic profile provided by the pore lumen drives this species toward the cytoplasm for protonation just before reaching the newly discovered site