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G D Shockman

Publications and source records attributed to G D Shockman.

114 records · Page 7Linked to original sources
PubMed1965

Replacement of Lysine by Hydroxylysine and Its Effects on Cell Lysis in Streptococcus faecalis.

Shockman, Gerald D. (Temple University, Philadelphia, Pa.), J. Stuart Thompson, and Margaret J. Conover. Replacement of lysine by hydroxylysine and its effects on cell lysis in Streptococcus faecalis. J. Bacteriol. 90:575-588. 1965.-Hydroxylysine was not significantly incorporated by Streptococcus faecalis ATCC 9790 or 8043 until exponential growth ceased as a result of lysine exhaustion. Uptake was then rapid and virtually complete within 1 hr. Lysine absence, rather than physiological age, seemed to be the governing factor. Hydroxylysine uptake rapidly reached a peak in the acid-soluble fraction, suggesting a precursor role for substances in this fraction. Substitution of hydroxylysine for lysine was much more efficient in mucopeptide synthesis than in protein synthesis. In wall medium, less than 1% of the incorporated hydroxylysine was found in the protein fraction. Addition of lysine to both growth and wall media inhibited both further hydroxylysine uptake and transfer of hydroxylysine from acid-soluble to mucopeptide or protein fractions. Hydroxylysine resulted in decreased penicillin susceptibility only after it was postexponentially incorporated. This effect was physiologically similar to that seen after threonine deprivation or chloramphenicol treatment. Hydroxylysine incorporation increased resistance to autolysis, but failed to decrease lysozyme susceptibility when measured after heat inactivation of autolysis. Electron microscopy of negatively stained cells showed increased thickness of cell walls containing hydroxylysine. Thus, most of the effects of replacement of lysine by hydroxylysine resemble those seen after deprivation of a nonwall amino acid (e.g., threonine or valine) or after chloramphenicol treatment. Each of these conditions results in inhibition of protein synthesis while permitting cell-wall synthesis to continue, resulting in autolysis-resistant, thick-walled cells.

Journal Article↗
PubMedDate not supplied

The autolytic peptidoglycan hydrolases of Streptococcus faecium.

Streptococcus faecium ATCC 9790 possesses two peptidoglycan hydrolase activities. The first enzyme, an N-acetylmuramoylhydrolase, has been purified and has been shown to be a glucoenzyme. Studies of hydrolysis of soluble, linear uncross-linked peptidoglycan chains showed that the enzyme bound strongly to the non-reducing ends of the chains and then sequentially (processively) hydrolysed susceptible bonds in that chain. The second peptidoglycan hydrolase does not appear to be a glycoprotein and differs from the first enzyme in substrate specificity and mechanism of hydrolysis. The presence of two partially redundant activities which may play different roles in surface growth and division could, at least in part, explain previous difficulties in obtaining mutants which completely lack autolytic activity.

Amidohydrolases↗
PubMedDate not supplied

Does penicillin kill bacteria?.

The thesis is presented that the bactericidal action of penicillin and of other inhibitors of cell wall peptidoglycan synthesis, such as vancomycin and cycloserine, is secondary or tertiary to their ability inhibit specific reactions in the assembly of an osmotically protective cell wall. Examples are given of the inhibition of these reactions, which results in inhibition of cell growth (bacteriostatic action) in the absence of either cellular lysis or rapid loss of viability. Thus, in some instances, inhibitory concentrations of these drugs are, in effect, sublethal; this is true, for example, for Streptococcus mutans, a species of bacteria that is part of the normal flora of the oropharynx and that can cause subacute bacterial endocarditis. On the other hand, the damaging effects of the subminimal inhibitory concentrations of penicillin G on Streptococcus faecalis, a species with an active autolytic enzyme system, can be uncovered and converted to a lytic (and lethal) response by partial inhibition of fatty acid synthesis with low concentrations of cerulenin. Some theoretical and practical implications of the occurrence and inhibition of these secondary lethal consequences are discussed.

Bacteria↗